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 $168.61   12.862%   $190.2966   $190.30   $190.30   $190.30  
  Purchase #2 $122.88   3.291%   $126.924   $126.92   $126.90   $126.90  
  Purchase #3 $59.39   4.583%   $62.1118   $62.11   $62.10   $62.10  
  Purchase #4 $45.68   13.199%   $51.7093   $51.71   $51.70   $51.70  
  Purchase #5 $129.81   6.568%   $138.3359   $138.34   $138.35   $138.30  
  Purchase #6 $103.90   10.336%   $114.6391   $114.64   $114.65   $114.60  
  Purchase #7 $10.95   7.450%   $11.7658   $11.77   $11.75   $11.80  
  7 purchase totals = $641.22       $695.7825   $695.79   $695.75   $695.70