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 $141.67   8.267%   $153.3819   $153.38   $153.40   $153.40  
  Purchase #2 $15.80   13.550%   $17.9409   $17.94   $17.95   $17.90  
  Purchase #3 $7.31   11.216%   $8.1299   $8.13   $8.15   $8.10  
  Purchase #4 $39.78   8.380%   $43.1136   $43.11   $43.10   $43.10  
  Purchase #5 $143.42   9.553%   $157.1209   $157.12   $157.10   $157.10  
  Purchase #6 $12.82   12.812%   $14.4625   $14.46   $14.45   $14.50  
  Purchase #7 $230.57   5.206%   $242.5735   $242.57   $242.55   $242.60  
  7 purchase totals = $591.37       $636.7232   $636.71   $636.70   $636.70