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 $41.53   13.617%   $47.1851   $47.19   $47.20   $47.20  
  Purchase #2 $141.77   5.817%   $150.0168   $150.02   $150.00   $150.00  
  Purchase #3 $9.33   10.743%   $10.3323   $10.33   $10.35   $10.30  
  Purchase #4 $221.51   13.152%   $250.643   $250.64   $250.65   $250.60  
  Purchase #5 $71.38   5.590%   $75.3701   $75.37   $75.35   $75.40  
  Purchase #6 $162.82   10.124%   $179.3039   $179.30   $179.30   $179.30  
  Purchase #7 $216.74   3.698%   $224.755   $224.76   $224.75   $224.80  
  7 purchase totals = $865.08       $937.6062   $937.61   $937.60   $937.60