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 $54.25   11.245%   $60.3504   $60.35   $60.35   $60.40  
  Purchase #2 $63.71   11.394%   $70.9691   $70.97   $70.95   $71.00  
  Purchase #3 $120.74   13.305%   $136.8045   $136.80   $136.80   $136.80  
  Purchase #4 $95.37   4.311%   $99.4814   $99.48   $99.50   $99.50  
  Purchase #5 $249.49   13.234%   $282.5075   $282.51   $282.50   $282.50  
  Purchase #6 $44.31   7.644%   $47.6971   $47.70   $47.70   $47.70  
  Purchase #7 $174.76   11.438%   $194.749   $194.75   $194.75   $194.70  
  7 purchase totals = $802.63       $892.5590   $892.56   $892.55   $892.60