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 $241.83   10.370%   $266.9078   $266.91   $266.90   $266.90  
  Purchase #2 $157.31   6.562%   $167.6327   $167.63   $167.65   $167.60  
  Purchase #3 $215.72   5.754%   $228.1325   $228.13   $228.15   $228.10  
  Purchase #4 $54.38   11.714%   $60.7501   $60.75   $60.75   $60.80  
  Purchase #5 $55.38   5.220%   $58.2708   $58.27   $58.25   $58.30  
  Purchase #6 $115.64   10.302%   $127.5532   $127.55   $127.55   $127.60  
  Purchase #7 $250.42   6.497%   $266.6898   $266.69   $266.70   $266.70  
  7 purchase totals = $1,090.68       $1,175.9369   $1,175.93   $1,175.95   $1,176.00