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 $242.83   10.377%   $268.0285   $268.03   $268.05   $268.00  
  Purchase #2 $45.29   10.196%   $49.9078   $49.91   $49.90   $49.90  
  Purchase #3 $62.72   7.302%   $67.2998   $67.30   $67.30   $67.30  
  Purchase #4 $163.38   13.646%   $185.6748   $185.67   $185.65   $185.70  
  Purchase #5 $48.34   8.844%   $52.6152   $52.62   $52.60   $52.60  
  Purchase #6 $217.80   6.491%   $231.9374   $231.94   $231.95   $231.90  
  Purchase #7 $67.67   8.267%   $73.2643   $73.26   $73.25   $73.30  
  7 purchase totals = $848.03       $928.7278   $928.73   $928.70   $928.70