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 $91.47   3.611%   $94.773   $94.77   $94.75   $94.80  
  Purchase #2 $26.79   11.639%   $29.9081   $29.91   $29.90   $29.90  
  Purchase #3 $171.42   13.659%   $194.8343   $194.83   $194.85   $194.80  
  Purchase #4 $168.31   4.305%   $175.5557   $175.56   $175.55   $175.60  
  Purchase #5 $57.66   7.723%   $62.1131   $62.11   $62.10   $62.10  
  Purchase #6 $180.54   10.489%   $199.4768   $199.48   $199.50   $199.50  
  Purchase #7 $173.82   9.367%   $190.1017   $190.10   $190.10   $190.10  
  7 purchase totals = $870.01       $946.7627   $946.76   $946.75   $946.80