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 $50.82   3.220%   $52.4564   $52.46   $52.45   $52.50  
  Purchase #2 $247.76   9.400%   $271.0494   $271.05   $271.05   $271.00  
  Purchase #3 $55.57   12.502%   $62.5174   $62.52   $62.50   $62.50  
  Purchase #4 $110.53   12.643%   $124.5043   $124.50   $124.50   $124.50  
  Purchase #5 $109.52   11.198%   $121.784   $121.78   $121.80   $121.80  
  Purchase #6 $99.48   5.687%   $105.1374   $105.14   $105.15   $105.10  
  Purchase #7 $206.81   3.619%   $214.2945   $214.29   $214.30   $214.30  
  7 purchase totals = $880.49       $951.7434   $951.74   $951.75   $951.70