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 $74.64   10.113%   $82.1883   $82.19   $82.20   $82.20  
  Purchase #2 $188.55   11.376%   $209.9994   $210.00   $210.00   $210.00  
  Purchase #3 $96.27   13.559%   $109.3232   $109.32   $109.30   $109.30  
  Purchase #4 $177.65   4.146%   $185.0154   $185.02   $185.00   $185.00  
  Purchase #5 $84.89   11.381%   $94.5513   $94.55   $94.55   $94.60  
  Purchase #6 $216.51   10.837%   $239.9732   $239.97   $239.95   $240.00  
  Purchase #7 $32.53   7.293%   $34.9024   $34.90   $34.90   $34.90  
  7 purchase totals = $871.04       $955.9532   $955.95   $955.90   $956.00