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 $48.44   7.731%   $52.1849   $52.18   $52.20   $52.20  
  Purchase #2 $248.79   5.429%   $262.2968   $262.30   $262.30   $262.30  
  Purchase #3 $131.47   13.317%   $148.9779   $148.98   $149.00   $149.00  
  Purchase #4 $26.26   6.557%   $27.9819   $27.98   $28.00   $28.00  
  Purchase #5 $203.98   13.325%   $231.1603   $231.16   $231.15   $231.20  
  Purchase #6 $147.99   11.184%   $164.5412   $164.54   $164.55   $164.50  
  Purchase #7 $126.53   11.827%   $141.4947   $141.49   $141.50   $141.50  
  7 purchase totals = $933.46       $1,028.6377   $1,028.63   $1,028.70   $1,028.70