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 $85.68   7.463%   $92.0743   $92.07   $92.05   $92.10  
  Purchase #2 $167.94   5.269%   $176.7888   $176.79   $176.80   $176.80  
  Purchase #3 $225.61   10.128%   $248.4598   $248.46   $248.45   $248.50  
  Purchase #4 $27.36   12.348%   $30.7384   $30.74   $30.75   $30.70  
  Purchase #5 $106.28   5.616%   $112.2487   $112.25   $112.25   $112.20  
  Purchase #6 $207.48   11.694%   $231.7427   $231.74   $231.75   $231.70  
  Purchase #7 $62.32   5.532%   $65.7675   $65.77   $65.75   $65.80  
  7 purchase totals = $882.67       $957.8202   $957.82   $957.80   $957.80