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 $246.63   5.817%   $260.9765   $260.98   $261.00   $261.00  
  Purchase #2 $165.64   6.261%   $176.0107   $176.01   $176.00   $176.00  
  Purchase #3 $69.45   5.263%   $73.1052   $73.11   $73.10   $73.10  
  Purchase #4 $14.37   11.822%   $16.0688   $16.07   $16.05   $16.10  
  Purchase #5 $136.52   7.176%   $146.3167   $146.32   $146.30   $146.30  
  Purchase #6 $118.26   9.541%   $129.5432   $129.54   $129.55   $129.50  
  Purchase #7 $62.80   7.211%   $67.3285   $67.33   $67.35   $67.30  
  7 purchase totals = $813.67       $869.3496   $869.36   $869.35   $869.30