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 $113.98   4.826%   $119.4807   $119.48   $119.50   $119.50  
  Purchase #2 $14.67   8.434%   $15.9073   $15.91   $15.90   $15.90  
  Purchase #3 $112.38   11.746%   $125.5802   $125.58   $125.60   $125.60  
  Purchase #4 $247.80   5.567%   $261.595   $261.60   $261.60   $261.60  
  Purchase #5 $128.96   11.605%   $143.9258   $143.93   $143.95   $143.90  
  Purchase #6 $219.66   9.457%   $240.4332   $240.43   $240.45   $240.40  
  Purchase #7 $59.94   6.184%   $63.6467   $63.65   $63.65   $63.60  
  7 purchase totals = $897.39       $970.5689   $970.58   $970.65   $970.50