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 $121.78   11.655%   $135.9735   $135.97   $135.95   $136.00  
  Purchase #2 $193.45   6.634%   $206.2835   $206.28   $206.30   $206.30  
  Purchase #3 $189.28   11.198%   $210.4756   $210.48   $210.50   $210.50  
  Purchase #4 $117.33   13.211%   $132.8305   $132.83   $132.85   $132.80  
  Purchase #5 $194.91   10.746%   $215.855   $215.86   $215.85   $215.90  
  Purchase #6 $223.71   12.657%   $252.025   $252.03   $252.05   $252.00  
  Purchase #7 $37.49   9.840%   $41.179   $41.18   $41.20   $41.20  
  7 purchase totals = $1,077.95       $1,194.6221   $1,194.63   $1,194.70   $1,194.70