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 $66.45   12.142%   $74.5184   $74.52   $74.50   $74.50  
  Purchase #2 $59.92   11.735%   $66.9516   $66.95   $66.95   $67.00  
  Purchase #3 $71.31   6.727%   $76.107   $76.11   $76.10   $76.10  
  Purchase #4 $114.96   8.404%   $124.6212   $124.62   $124.60   $124.60  
  Purchase #5 $158.95   13.124%   $179.8106   $179.81   $179.80   $179.80  
  Purchase #6 $60.45   8.821%   $65.7823   $65.78   $65.80   $65.80  
  Purchase #7 $193.91   11.630%   $216.4617   $216.46   $216.45   $216.50  
  7 purchase totals = $725.95       $804.2528   $804.25   $804.20   $804.30