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 $74.57   13.393%   $84.5572   $84.56   $84.55   $84.60  
  Purchase #2 $68.96   12.250%   $77.4076   $77.41   $77.40   $77.40  
  Purchase #3 $58.59   11.599%   $65.3859   $65.39   $65.40   $65.40  
  Purchase #4 $203.37   10.574%   $224.8743   $224.87   $224.85   $224.90  
  Purchase #5 $59.80   10.704%   $66.201   $66.20   $66.20   $66.20  
  Purchase #6 $112.42   8.478%   $121.951   $121.95   $121.95   $122.00  
  Purchase #7 $85.97   5.768%   $90.9287   $90.93   $90.95   $90.90  
  7 purchase totals = $663.68       $731.3057   $731.31   $731.30   $731.40