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 $105.45   13.312%   $119.4875   $119.49   $119.50   $119.50  
  Purchase #2 $109.85   3.755%   $113.9749   $113.97   $113.95   $114.00  
  Purchase #3 $232.69   3.851%   $241.6509   $241.65   $241.65   $241.70  
  Purchase #4 $18.56   7.507%   $19.9533   $19.95   $19.95   $20.00  
  Purchase #5 $178.61   9.544%   $195.6565   $195.66   $195.65   $195.70  
  Purchase #6 $61.66   6.248%   $65.5125   $65.51   $65.50   $65.50  
  Purchase #7 $5.45   8.609%   $5.9192   $5.92   $5.90   $5.90  
  7 purchase totals = $712.27       $762.1548   $762.15   $762.10   $762.30