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 $62.64   8.171%   $67.7583   $67.76   $67.75   $67.80  
  Purchase #2 $249.31   7.708%   $268.5268   $268.53   $268.55   $268.50  
  Purchase #3 $245.76   10.365%   $271.233   $271.23   $271.25   $271.20  
  Purchase #4 $140.91   3.841%   $146.3224   $146.32   $146.30   $146.30  
  Purchase #5 $249.78   3.682%   $258.9769   $258.98   $259.00   $259.00  
  Purchase #6 $176.37   8.775%   $191.8465   $191.85   $191.85   $191.80  
  Purchase #7 $10.64   13.134%   $12.0375   $12.04   $12.05   $12.00  
  7 purchase totals = $1,135.41       $1,216.7014   $1,216.71   $1,216.75   $1,216.60