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 $184.94   8.863%   $201.3312   $201.33   $201.35   $201.30  
  Purchase #2 $90.70   7.686%   $97.6712   $97.67   $97.65   $97.70  
  Purchase #3 $62.41   8.641%   $67.8028   $67.80   $67.80   $67.80  
  Purchase #4 $244.57   12.346%   $274.7646   $274.76   $274.75   $274.80  
  Purchase #5 $68.72   4.218%   $71.6186   $71.62   $71.60   $71.60  
  Purchase #6 $146.54   11.632%   $163.5855   $163.59   $163.60   $163.60  
  Purchase #7 $53.42   11.549%   $59.5895   $59.59   $59.60   $59.60  
  7 purchase totals = $851.30       $936.3634   $936.36   $936.35   $936.40