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 $76.33   4.739%   $79.9473   $79.95   $79.95   $79.90  
  Purchase #2 $248.97   11.127%   $276.6729   $276.67   $276.65   $276.70  
  Purchase #3 $66.46   13.444%   $75.3949   $75.39   $75.40   $75.40  
  Purchase #4 $56.97   11.871%   $63.7329   $63.73   $63.75   $63.70  
  Purchase #5 $55.86   12.612%   $62.9051   $62.91   $62.90   $62.90  
  Purchase #6 $123.69   12.605%   $139.2811   $139.28   $139.30   $139.30  
  Purchase #7 $96.37   3.107%   $99.3642   $99.36   $99.35   $99.40  
  7 purchase totals = $724.65       $797.2984   $797.29   $797.30   $797.30