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 $86.72   13.377%   $98.3205   $98.32   $98.30   $98.30  
  Purchase #2 $175.74   11.193%   $195.4106   $195.41   $195.40   $195.40  
  Purchase #3 $176.79   6.548%   $188.3662   $188.37   $188.35   $188.40  
  Purchase #4 $229.50   13.175%   $259.7366   $259.74   $259.75   $259.70  
  Purchase #5 $102.25   10.513%   $112.9995   $113.00   $113.00   $113.00  
  Purchase #6 $248.56   7.121%   $266.26   $266.26   $266.25   $266.30  
  Purchase #7 $167.41   12.220%   $187.8675   $187.87   $187.85   $187.90  
  7 purchase totals = $1,186.97       $1,308.9609   $1,308.97   $1,308.90   $1,309.00