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 $95.44   3.669%   $98.9417   $98.94   $98.95   $98.90  
  Purchase #2 $112.93   4.149%   $117.6155   $117.62   $117.60   $117.60  
  Purchase #3 $38.57   10.573%   $42.648   $42.65   $42.65   $42.60  
  Purchase #4 $84.37   11.801%   $94.3265   $94.33   $94.35   $94.30  
  Purchase #5 $111.95   12.339%   $125.7635   $125.76   $125.75   $125.80  
  Purchase #6 $96.47   10.831%   $106.9187   $106.92   $106.90   $106.90  
  Purchase #7 $64.79   13.535%   $73.5593   $73.56   $73.55   $73.60  
  7 purchase totals = $604.52       $659.7732   $659.78   $659.75   $659.70