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 $243.47   9.768%   $267.2521   $267.25   $267.25   $267.30  
  Purchase #2 $81.91   12.295%   $91.9808   $91.98   $92.00   $92.00  
  Purchase #3 $65.54   11.658%   $73.1807   $73.18   $73.20   $73.20  
  Purchase #4 $24.35   12.380%   $27.3645   $27.36   $27.35   $27.40  
  Purchase #5 $118.81   8.795%   $129.2593   $129.26   $129.25   $129.30  
  Purchase #6 $165.70   12.223%   $185.9535   $185.95   $185.95   $186.00  
  Purchase #7 $170.45   9.404%   $186.4791   $186.48   $186.50   $186.50  
  7 purchase totals = $870.23       $961.4700   $961.46   $961.50   $961.70