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 $194.70   12.359%   $218.763   $218.76   $218.75   $218.80  
  Purchase #2 $18.42   10.417%   $20.3388   $20.34   $20.35   $20.30  
  Purchase #3 $11.90   8.151%   $12.87   $12.87   $12.85   $12.90  
  Purchase #4 $163.26   10.701%   $180.7305   $180.73   $180.75   $180.70  
  Purchase #5 $201.47   11.375%   $224.3872   $224.39   $224.40   $224.40  
  Purchase #6 $26.91   4.672%   $28.1672   $28.17   $28.15   $28.20  
  Purchase #7 $108.60   8.251%   $117.5606   $117.56   $117.55   $117.60  
  7 purchase totals = $725.26       $802.8173   $802.82   $802.80   $802.90