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 $197.88   5.518%   $208.799   $208.80   $208.80   $208.80  
  Purchase #2 $59.98   4.667%   $62.7793   $62.78   $62.80   $62.80  
  Purchase #3 $57.36   9.830%   $62.9985   $63.00   $63.00   $63.00  
  Purchase #4 $9.87   3.561%   $10.2215   $10.22   $10.20   $10.20  
  Purchase #5 $30.50   12.706%   $34.3753   $34.38   $34.40   $34.40  
  Purchase #6 $247.35   7.838%   $266.7373   $266.74   $266.75   $266.70  
  Purchase #7 $132.35   12.411%   $148.776   $148.78   $148.80   $148.80  
  7 purchase totals = $735.29       $794.6869   $794.70   $794.75   $794.70