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 $170.26   11.108%   $189.1725   $189.17   $189.15   $189.20  
  Purchase #2 $182.48   12.691%   $205.6385   $205.64   $205.65   $205.60  
  Purchase #3 $58.25   6.677%   $62.1394   $62.14   $62.15   $62.10  
  Purchase #4 $130.45   11.355%   $145.2626   $145.26   $145.25   $145.30  
  Purchase #5 $5.57   7.240%   $5.9733   $5.97   $5.95   $6.00  
  Purchase #6 $23.26   12.852%   $26.2494   $26.25   $26.25   $26.20  
  Purchase #7 $83.96   8.659%   $91.2301   $91.23   $91.25   $91.20  
  7 purchase totals = $654.23       $725.6658   $725.66   $725.65   $725.60