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 $224.79   11.229%   $250.0317   $250.03   $250.05   $250.00  
  Purchase #2 $203.41   8.695%   $221.0965   $221.10   $221.10   $221.10  
  Purchase #3 $44.55   3.802%   $46.2438   $46.24   $46.25   $46.20  
  Purchase #4 $175.71   13.355%   $199.1761   $199.18   $199.20   $199.20  
  Purchase #5 $104.84   6.591%   $111.75   $111.75   $111.75   $111.80  
  Purchase #6 $58.85   3.324%   $60.8062   $60.81   $60.80   $60.80  
  Purchase #7 $75.82   3.413%   $78.4077   $78.41   $78.40   $78.40  
  7 purchase totals = $887.97       $967.5120   $967.52   $967.55   $967.50