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 $46.42   6.214%   $49.3045   $49.30   $49.30   $49.30  
  Purchase #2 $121.43   4.389%   $126.7596   $126.76   $126.75   $126.80  
  Purchase #3 $196.66   3.842%   $204.2157   $204.22   $204.20   $204.20  
  Purchase #4 $140.88   7.428%   $151.3446   $151.34   $151.35   $151.30  
  Purchase #5 $245.82   13.754%   $279.6301   $279.63   $279.65   $279.60  
  Purchase #6 $29.67   7.870%   $32.005   $32.01   $32.00   $32.00  
  Purchase #7 $199.50   6.346%   $212.1603   $212.16   $212.15   $212.20  
  7 purchase totals = $980.38       $1,055.4198   $1,055.42   $1,055.40   $1,055.40