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 $144.42   8.725%   $157.0206   $157.02   $157.00   $157.00  
  Purchase #2 $91.97   11.766%   $102.7912   $102.79   $102.80   $102.80  
  Purchase #3 $62.56   12.110%   $70.136   $70.14   $70.15   $70.10  
  Purchase #4 $85.27   6.163%   $90.5252   $90.53   $90.55   $90.50  
  Purchase #5 $250.28   3.590%   $259.2651   $259.27   $259.25   $259.30  
  Purchase #6 $68.45   3.666%   $70.9594   $70.96   $70.95   $71.00  
  Purchase #7 $173.46   12.576%   $195.2743   $195.27   $195.25   $195.30  
  7 purchase totals = $876.41       $945.9718   $945.98   $945.95   $946.00