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 $113.84   4.814%   $119.3203   $119.32   $119.30   $119.30  
  Purchase #2 $15.95   9.132%   $17.4066   $17.41   $17.40   $17.40  
  Purchase #3 $197.62   8.266%   $213.9553   $213.96   $213.95   $214.00  
  Purchase #4 $33.50   6.770%   $35.768   $35.77   $35.75   $35.80  
  Purchase #5 $49.35   7.195%   $52.9007   $52.90   $52.90   $52.90  
  Purchase #6 $189.69   9.212%   $207.1642   $207.16   $207.15   $207.20  
  Purchase #7 $150.66   7.475%   $161.9218   $161.92   $161.90   $161.90  
  7 purchase totals = $750.61       $808.4369   $808.44   $808.35   $808.50