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 $222.87   11.195%   $247.8203   $247.82   $247.80   $247.80  
  Purchase #2 $46.97   11.388%   $52.3189   $52.32   $52.30   $52.30  
  Purchase #3 $56.71   7.462%   $60.9417   $60.94   $60.95   $60.90  
  Purchase #4 $239.61   5.566%   $252.9467   $252.95   $252.95   $252.90  
  Purchase #5 $32.34   5.853%   $34.2329   $34.23   $34.25   $34.20  
  Purchase #6 $111.73   5.362%   $117.721   $117.72   $117.70   $117.70  
  Purchase #7 $135.78   6.715%   $144.8976   $144.90   $144.90   $144.90  
  7 purchase totals = $846.01       $910.8791   $910.88   $910.85   $910.70