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 $36.86   13.276%   $41.7535   $41.75   $41.75   $41.80  
  Purchase #2 $162.94   4.549%   $170.3521   $170.35   $170.35   $170.40  
  Purchase #3 $202.72   12.793%   $228.654   $228.65   $228.65   $228.70  
  Purchase #4 $21.70   12.102%   $24.3261   $24.33   $24.35   $24.30  
  Purchase #5 $59.45   10.193%   $65.5097   $65.51   $65.50   $65.50  
  Purchase #6 $50.56   5.847%   $53.5162   $53.52   $53.50   $53.50  
  Purchase #7 $154.72   9.853%   $169.9646   $169.96   $169.95   $170.00  
  7 purchase totals = $688.95       $754.0762   $754.07   $754.05   $754.20