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 $141.59   11.775%   $158.2622   $158.26   $158.25   $158.30  
  Purchase #2 $35.27   10.523%   $38.9815   $38.98   $39.00   $39.00  
  Purchase #3 $212.62   6.533%   $226.5105   $226.51   $226.50   $226.50  
  Purchase #4 $73.46   4.234%   $76.5703   $76.57   $76.55   $76.60  
  Purchase #5 $226.55   6.338%   $240.9087   $240.91   $240.90   $240.90  
  Purchase #6 $169.48   11.601%   $189.1414   $189.14   $189.15   $189.10  
  Purchase #7 $51.43   7.431%   $55.2518   $55.25   $55.25   $55.30  
  7 purchase totals = $910.40       $985.6264   $985.62   $985.60   $985.70