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 $63.53   13.244%   $71.9439   $71.94   $71.95   $71.90  
  Purchase #2 $157.66   5.780%   $166.7727   $166.77   $166.75   $166.80  
  Purchase #3 $201.48   13.746%   $229.1754   $229.18   $229.20   $229.20  
  Purchase #4 $159.38   7.236%   $170.9127   $170.91   $170.90   $170.90  
  Purchase #5 $28.92   10.415%   $31.932   $31.93   $31.95   $31.90  
  Purchase #6 $51.52   3.683%   $53.4175   $53.42   $53.40   $53.40  
  Purchase #7 $168.69   9.444%   $184.6211   $184.62   $184.60   $184.60  
  7 purchase totals = $831.18       $908.7753   $908.77   $908.75   $908.70