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 $193.65   4.781%   $202.9084   $202.91   $202.90   $202.90  
  Purchase #2 $51.87   5.574%   $54.7612   $54.76   $54.75   $54.80  
  Purchase #3 $73.82   13.140%   $83.5199   $83.52   $83.50   $83.50  
  Purchase #4 $186.30   4.555%   $194.786   $194.79   $194.80   $194.80  
  Purchase #5 $113.62   9.783%   $124.7354   $124.74   $124.75   $124.70  
  Purchase #6 $118.63   10.123%   $130.6389   $130.64   $130.65   $130.60  
  Purchase #7 $106.70   4.282%   $111.2689   $111.27   $111.25   $111.30  
  7 purchase totals = $844.59       $902.6187   $902.63   $902.60   $902.60