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 $195.30   6.756%   $208.4945   $208.49   $208.50   $208.50  
  Purchase #2 $194.78   5.213%   $204.9339   $204.93   $204.95   $204.90  
  Purchase #3 $84.37   5.552%   $89.0542   $89.05   $89.05   $89.10  
  Purchase #4 $98.50   4.371%   $102.8054   $102.81   $102.80   $102.80  
  Purchase #5 $250.46   6.298%   $266.234   $266.23   $266.25   $266.20  
  Purchase #6 $60.96   9.467%   $66.7311   $66.73   $66.75   $66.70  
  Purchase #7 $22.98   7.145%   $24.6219   $24.62   $24.60   $24.60  
  7 purchase totals = $907.35       $962.8750   $962.86   $962.90   $962.80