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 $92.65   12.542%   $104.2702   $104.27   $104.25   $104.30  
  Purchase #2 $66.81   13.185%   $75.6189   $75.62   $75.60   $75.60  
  Purchase #3 $150.33   3.688%   $155.8742   $155.87   $155.85   $155.90  
  Purchase #4 $129.66   9.757%   $142.3109   $142.31   $142.30   $142.30  
  Purchase #5 $147.62   5.857%   $156.2661   $156.27   $156.25   $156.30  
  Purchase #6 $68.71   8.362%   $74.4555   $74.46   $74.45   $74.50  
  Purchase #7 $90.73   7.461%   $97.4994   $97.50   $97.50   $97.50  
  7 purchase totals = $746.51       $806.2952   $806.30   $806.20   $806.40