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 $58.83   9.253%   $64.2735   $64.27   $64.25   $64.30  
  Purchase #2 $227.78   10.183%   $250.9748   $250.97   $250.95   $251.00  
  Purchase #3 $44.68   3.285%   $46.1477   $46.15   $46.15   $46.10  
  Purchase #4 $76.44   10.558%   $84.5105   $84.51   $84.50   $84.50  
  Purchase #5 $57.52   5.803%   $60.8579   $60.86   $60.85   $60.90  
  Purchase #6 $147.77   7.673%   $159.1084   $159.11   $159.10   $159.10  
  Purchase #7 $113.96   13.263%   $129.0745   $129.07   $129.05   $129.10  
  7 purchase totals = $726.98       $794.9473   $794.94   $794.85   $795.00