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 $58.91   13.270%   $66.7274   $66.73   $66.75   $66.70  
  Purchase #2 $195.58   4.822%   $205.0109   $205.01   $205.00   $205.00  
  Purchase #3 $136.28   12.333%   $153.0874   $153.09   $153.10   $153.10  
  Purchase #4 $157.87   9.802%   $173.3444   $173.34   $173.35   $173.30  
  Purchase #5 $62.68   3.561%   $64.912   $64.91   $64.90   $64.90  
  Purchase #6 $128.42   5.388%   $135.3393   $135.34   $135.35   $135.30  
  Purchase #7 $129.46   4.777%   $135.6443   $135.64   $135.65   $135.60  
  7 purchase totals = $869.20       $934.0657   $934.06   $934.10   $933.90