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 $188.49   10.753%   $208.7583   $208.76   $208.75   $208.80  
  Purchase #2 $7.26   5.818%   $7.6824   $7.68   $7.70   $7.70  
  Purchase #3 $95.77   6.413%   $101.9117   $101.91   $101.90   $101.90  
  Purchase #4 $249.67   11.374%   $278.0675   $278.07   $278.05   $278.10  
  Purchase #5 $95.41   10.703%   $105.6217   $105.62   $105.60   $105.60  
  Purchase #6 $130.64   10.450%   $144.2919   $144.29   $144.30   $144.30  
  Purchase #7 $87.43   12.464%   $98.3273   $98.33   $98.35   $98.30  
  7 purchase totals = $854.67       $944.6608   $944.66   $944.65   $944.70