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 $53.98   13.440%   $61.2349   $61.23   $61.25   $61.20  
  Purchase #2 $187.30   9.353%   $204.8182   $204.82   $204.80   $204.80  
  Purchase #3 $113.78   10.780%   $126.0455   $126.05   $126.05   $126.00  
  Purchase #4 $79.76   4.643%   $83.4633   $83.46   $83.45   $83.50  
  Purchase #5 $62.85   12.669%   $70.8125   $70.81   $70.80   $70.80  
  Purchase #6 $97.87   4.414%   $102.19   $102.19   $102.20   $102.20  
  Purchase #7 $244.78   9.233%   $267.3805   $267.38   $267.40   $267.40  
  7 purchase totals = $840.32       $915.9449   $915.94   $915.95   $915.90