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 $63.34   13.102%   $71.6388   $71.64   $71.65   $71.60  
  Purchase #2 $47.93   4.870%   $50.2642   $50.26   $50.25   $50.30  
  Purchase #3 $202.64   11.684%   $226.3165   $226.32   $226.30   $226.30  
  Purchase #4 $228.65   7.237%   $245.1974   $245.20   $245.20   $245.20  
  Purchase #5 $174.38   7.787%   $187.959   $187.96   $187.95   $188.00  
  Purchase #6 $92.73   9.600%   $101.6321   $101.63   $101.65   $101.60  
  Purchase #7 $74.58   13.785%   $84.8609   $84.86   $84.85   $84.90  
  7 purchase totals = $884.25       $967.8689   $967.87   $967.85   $967.90