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 $112.73   12.599%   $126.9329   $126.93   $126.95   $126.90  
  Purchase #2 $144.84   5.539%   $152.8627   $152.86   $152.85   $152.90  
  Purchase #3 $66.48   7.123%   $71.2154   $71.22   $71.20   $71.20  
  Purchase #4 $125.76   12.519%   $141.5039   $141.50   $141.50   $141.50  
  Purchase #5 $242.83   6.335%   $258.2133   $258.21   $258.20   $258.20  
  Purchase #6 $10.89   5.297%   $11.4668   $11.47   $11.45   $11.50  
  Purchase #7 $204.50   7.473%   $219.7823   $219.78   $219.80   $219.80  
  7 purchase totals = $908.03       $981.9773   $981.97   $981.95   $982.00