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 $82.43   11.792%   $92.1501   $92.15   $92.15   $92.20  
  Purchase #2 $167.50   13.854%   $190.7055   $190.71   $190.70   $190.70  
  Purchase #3 $129.81   3.149%   $133.8977   $133.90   $133.90   $133.90  
  Purchase #4 $69.46   3.400%   $71.8216   $71.82   $71.80   $71.80  
  Purchase #5 $204.41   3.174%   $210.898   $210.90   $210.90   $210.90  
  Purchase #6 $19.63   13.428%   $22.2659   $22.27   $22.25   $22.30  
  Purchase #7 $169.71   11.406%   $189.0671   $189.07   $189.05   $189.10  
  7 purchase totals = $842.95       $910.8059   $910.82   $910.75   $910.90