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 $61.57   8.676%   $66.9118   $66.91   $66.90   $66.90  
  Purchase #2 $198.82   5.491%   $209.7372   $209.74   $209.75   $209.70  
  Purchase #3 $104.97   13.761%   $119.4149   $119.41   $119.40   $119.40  
  Purchase #4 $146.97   11.696%   $164.1596   $164.16   $164.15   $164.20  
  Purchase #5 $5.66   4.414%   $5.9098   $5.91   $5.90   $5.90  
  Purchase #6 $47.31   13.328%   $53.6155   $53.62   $53.60   $53.60  
  Purchase #7 $181.74   3.702%   $188.468   $188.47   $188.45   $188.50  
  7 purchase totals = $747.04       $808.2168   $808.22   $808.15   $808.20