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 $76.55   10.871%   $84.8718   $84.87   $84.85   $84.90  
  Purchase #2 $164.96   4.105%   $171.7316   $171.73   $171.75   $171.70  
  Purchase #3 $44.74   8.822%   $48.687   $48.69   $48.70   $48.70  
  Purchase #4 $89.41   9.331%   $97.7528   $97.75   $97.75   $97.80  
  Purchase #5 $213.73   6.162%   $226.9   $226.90   $226.90   $226.90  
  Purchase #6 $136.41   5.460%   $143.858   $143.86   $143.85   $143.90  
  Purchase #7 $197.45   9.642%   $216.4881   $216.49   $216.50   $216.50  
  7 purchase totals = $923.25       $990.2893   $990.29   $990.30   $990.40