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 $243.83   8.804%   $265.2968   $265.30   $265.30   $265.30  
  Purchase #2 $47.93   6.234%   $50.918   $50.92   $50.90   $50.90  
  Purchase #3 $51.64   11.620%   $57.6406   $57.64   $57.65   $57.60  
  Purchase #4 $232.48   6.388%   $247.3308   $247.33   $247.35   $247.30  
  Purchase #5 $83.85   10.350%   $92.5285   $92.53   $92.55   $92.50  
  Purchase #6 $75.94   4.177%   $79.112   $79.11   $79.10   $79.10  
  Purchase #7 $50.32   8.745%   $54.7205   $54.72   $54.70   $54.70  
  7 purchase totals = $785.99       $847.5472   $847.55   $847.55   $847.40