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 $236.36   13.380%   $267.985   $267.99   $268.00   $268.00  
  Purchase #2 $104.25   13.138%   $117.9464   $117.95   $117.95   $117.90  
  Purchase #3 $185.81   4.513%   $194.1956   $194.20   $194.20   $194.20  
  Purchase #4 $69.46   9.692%   $76.1921   $76.19   $76.20   $76.20  
  Purchase #5 $184.31   3.448%   $190.665   $190.67   $190.65   $190.70  
  Purchase #6 $130.25   5.240%   $137.0751   $137.08   $137.10   $137.10  
  Purchase #7 $48.53   4.501%   $50.7143   $50.71   $50.70   $50.70  
  7 purchase totals = $958.97       $1,034.7735   $1,034.79   $1,034.80   $1,034.80