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 $105.57   5.770%   $111.6614   $111.66   $111.65   $111.70  
  Purchase #2 $51.72   7.197%   $55.4423   $55.44   $55.45   $55.40  
  Purchase #3 $102.43   4.203%   $106.7351   $106.74   $106.75   $106.70  
  Purchase #4 $196.69   4.844%   $206.2177   $206.22   $206.20   $206.20  
  Purchase #5 $182.30   10.278%   $201.0368   $201.04   $201.05   $201.00  
  Purchase #6 $76.73   11.762%   $85.755   $85.76   $85.75   $85.80  
  Purchase #7 $165.69   10.742%   $183.4884   $183.49   $183.50   $183.50  
  7 purchase totals = $881.13       $950.3367   $950.35   $950.35   $950.30