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 $68.86   5.689%   $72.7774   $72.78   $72.80   $72.80  
  Purchase #2 $122.53   8.222%   $132.6044   $132.60   $132.60   $132.60  
  Purchase #3 $204.28   3.566%   $211.5646   $211.56   $211.55   $211.60  
  Purchase #4 $16.95   12.179%   $19.0143   $19.01   $19.00   $19.00  
  Purchase #5 $58.83   8.433%   $63.7911   $63.79   $63.80   $63.80  
  Purchase #6 $243.92   7.241%   $261.5822   $261.58   $261.60   $261.60  
  Purchase #7 $190.82   6.505%   $203.2328   $203.23   $203.25   $203.20  
  7 purchase totals = $906.19       $964.5668   $964.55   $964.60   $964.60