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 $213.35   8.512%   $231.5104   $231.51   $231.50   $231.50  
  Purchase #2 $226.62   7.308%   $243.1814   $243.18   $243.20   $243.20  
  Purchase #3 $119.90   12.310%   $134.6597   $134.66   $134.65   $134.70  
  Purchase #4 $173.64   13.551%   $197.17   $197.17   $197.15   $197.20  
  Purchase #5 $14.61   7.569%   $15.7158   $15.72   $15.70   $15.70  
  Purchase #6 $200.95   7.368%   $215.756   $215.76   $215.75   $215.80  
  Purchase #7 $197.45   9.326%   $215.8642   $215.86   $215.85   $215.90  
  7 purchase totals = $1,146.52       $1,253.8575   $1,253.86   $1,253.80   $1,254.00