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 $34.66   9.212%   $37.8529   $37.85   $37.85   $37.90  
  Purchase #2 $243.88   5.602%   $257.5422   $257.54   $257.55   $257.50  
  Purchase #3 $232.31   4.643%   $243.0962   $243.10   $243.10   $243.10  
  Purchase #4 $89.44   11.673%   $99.8803   $99.88   $99.90   $99.90  
  Purchase #5 $245.67   6.124%   $260.7148   $260.71   $260.70   $260.70  
  Purchase #6 $46.79   3.550%   $48.451   $48.45   $48.45   $48.50  
  Purchase #7 $217.76   7.684%   $234.4927   $234.49   $234.50   $234.50  
  7 purchase totals = $1,110.51       $1,182.0301   $1,182.02   $1,182.05   $1,182.10