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 $216.64   11.755%   $242.106   $242.11   $242.10   $242.10  
  Purchase #2 $175.44   11.649%   $195.877   $195.88   $195.90   $195.90  
  Purchase #3 $51.76   12.406%   $58.1813   $58.18   $58.20   $58.20  
  Purchase #4 $23.97   12.682%   $27.0099   $27.01   $27.00   $27.00  
  Purchase #5 $12.86   9.759%   $14.115   $14.12   $14.10   $14.10  
  Purchase #6 $74.71   3.374%   $77.2307   $77.23   $77.25   $77.20  
  Purchase #7 $34.92   4.733%   $36.5728   $36.57   $36.55   $36.60  
  7 purchase totals = $590.30       $651.0927   $651.10   $651.10   $651.10