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 $182.94   6.852%   $195.475   $195.48   $195.50   $195.50  
  Purchase #2 $140.39   3.253%   $144.9569   $144.96   $144.95   $145.00  
  Purchase #3 $241.69   7.508%   $259.8361   $259.84   $259.85   $259.80  
  Purchase #4 $209.33   5.472%   $220.7845   $220.78   $220.80   $220.80  
  Purchase #5 $201.83   3.663%   $209.223   $209.22   $209.20   $209.20  
  Purchase #6 $43.85   7.383%   $47.0874   $47.09   $47.10   $47.10  
  Purchase #7 $250.39   4.806%   $262.4237   $262.42   $262.40   $262.40  
  7 purchase totals = $1,270.42       $1,339.7866   $1,339.79   $1,339.80   $1,339.80