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 $78.49   8.163%   $84.8971   $84.90   $84.90   $84.90  
  Purchase #2 $207.80   4.425%   $216.9952   $217.00   $217.00   $217.00  
  Purchase #3 $131.71   4.644%   $137.8266   $137.83   $137.85   $137.80  
  Purchase #4 $26.89   9.369%   $29.4093   $29.41   $29.40   $29.40  
  Purchase #5 $10.41   5.772%   $11.0109   $11.01   $11.00   $11.00  
  Purchase #6 $216.31   9.565%   $237.0001   $237.00   $237.00   $237.00  
  Purchase #7 $211.47   3.130%   $218.089   $218.09   $218.10   $218.10  
  7 purchase totals = $883.08       $935.2282   $935.24   $935.25   $935.20