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 $36.35   13.846%   $41.383   $41.38   $41.40   $41.40  
  Purchase #2 $241.37   5.209%   $253.943   $253.94   $253.95   $253.90  
  Purchase #3 $174.47   8.455%   $189.2214   $189.22   $189.20   $189.20  
  Purchase #4 $59.65   6.384%   $63.4581   $63.46   $63.45   $63.50  
  Purchase #5 $174.28   4.738%   $182.5374   $182.54   $182.55   $182.50  
  Purchase #6 $62.34   9.654%   $68.3583   $68.36   $68.35   $68.40  
  Purchase #7 $44.78   6.375%   $47.6347   $47.63   $47.65   $47.60  
  7 purchase totals = $793.24       $846.5359   $846.53   $846.55   $846.50