Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.42   13.605%   $135.6671   $135.67   $135.65   $135.70  
  Purchase #2 $202.67   11.277%   $225.5251   $225.53   $225.55   $225.50  
  Purchase #3 $64.70   7.698%   $69.6806   $69.68   $69.70   $69.70  
  Purchase #4 $192.34   11.445%   $214.3533   $214.35   $214.35   $214.40  
  Purchase #5 $187.59   10.682%   $207.6284   $207.63   $207.65   $207.60  
  Purchase #6 $40.35   12.775%   $45.5047   $45.50   $45.50   $45.50  
  Purchase #7 $43.39   5.177%   $45.6363   $45.64   $45.65   $45.60  
  7 purchase totals = $850.46       $943.9955   $944.00   $944.05   $944.00