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 $213.85   10.731%   $236.7982   $236.80   $236.80   $236.80  
  Purchase #2 $241.41   12.288%   $271.0745   $271.07   $271.05   $271.10  
  Purchase #3 $205.82   10.594%   $227.6246   $227.62   $227.60   $227.60  
  Purchase #4 $25.56   6.379%   $27.1905   $27.19   $27.20   $27.20  
  Purchase #5 $185.73   11.403%   $206.9088   $206.91   $206.90   $206.90  
  Purchase #6 $184.65   6.663%   $196.9532   $196.95   $196.95   $197.00  
  Purchase #7 $244.59   6.461%   $260.393   $260.39   $260.40   $260.40  
  7 purchase totals = $1,301.61       $1,426.9428   $1,426.93   $1,426.90   $1,427.00