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 $184.69   13.151%   $208.9786   $208.98   $209.00   $209.00  
  Purchase #2 $171.86   8.149%   $185.8649   $185.86   $185.85   $185.90  
  Purchase #3 $105.47   12.848%   $119.0208   $119.02   $119.00   $119.00  
  Purchase #4 $133.34   12.376%   $149.8422   $149.84   $149.85   $149.80  
  Purchase #5 $241.73   10.110%   $266.1689   $266.17   $266.15   $266.20  
  Purchase #6 $67.87   10.598%   $75.0629   $75.06   $75.05   $75.10  
  Purchase #7 $229.30   7.297%   $246.032   $246.03   $246.05   $246.00  
  7 purchase totals = $1,134.26       $1,250.9703   $1,250.96   $1,250.95   $1,251.00