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 $183.97   13.401%   $208.6238   $208.62   $208.60   $208.60  
  Purchase #2 $245.82   8.144%   $265.8396   $265.84   $265.85   $265.80  
  Purchase #3 $105.79   7.411%   $113.6301   $113.63   $113.65   $113.60  
  Purchase #4 $91.25   5.171%   $95.9685   $95.97   $95.95   $96.00  
  Purchase #5 $160.95   6.624%   $171.6113   $171.61   $171.60   $171.60  
  Purchase #6 $15.41   3.235%   $15.9085   $15.91   $15.90   $15.90  
  Purchase #7 $119.33   10.594%   $131.9718   $131.97   $131.95   $132.00  
  7 purchase totals = $922.52       $1,003.5536   $1,003.55   $1,003.50   $1,003.50