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 $220.38   3.645%   $228.4129   $228.41   $228.40   $228.40  
  Purchase #2 $77.95   11.793%   $87.1426   $87.14   $87.15   $87.10  
  Purchase #3 $140.78   8.310%   $152.4788   $152.48   $152.50   $152.50  
  Purchase #4 $70.34   10.840%   $77.9649   $77.96   $77.95   $78.00  
  Purchase #5 $231.37   9.521%   $253.3987   $253.40   $253.40   $253.40  
  Purchase #6 $43.33   12.581%   $48.7813   $48.78   $48.80   $48.80  
  Purchase #7 $87.56   6.539%   $93.2855   $93.29   $93.30   $93.30  
  7 purchase totals = $871.71       $941.4647   $941.46   $941.50   $941.50