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 $195.67   3.402%   $202.3267   $202.33   $202.35   $202.30  
  Purchase #2 $90.90   5.167%   $95.5968   $95.60   $95.60   $95.60  
  Purchase #3 $44.35   11.722%   $49.5487   $49.55   $49.55   $49.50  
  Purchase #4 $97.37   13.366%   $110.3845   $110.38   $110.40   $110.40  
  Purchase #5 $206.60   3.607%   $214.0521   $214.05   $214.05   $214.10  
  Purchase #6 $84.62   10.386%   $93.4086   $93.41   $93.40   $93.40  
  Purchase #7 $125.37   9.795%   $137.65   $137.65   $137.65   $137.70  
  7 purchase totals = $844.88       $902.9674   $902.97   $903.00   $903.00