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 $229.67   5.348%   $241.9528   $241.95   $241.95   $242.00  
  Purchase #2 $44.26   12.554%   $49.8164   $49.82   $49.80   $49.80  
  Purchase #3 $16.93   8.181%   $18.315   $18.32   $18.30   $18.30  
  Purchase #4 $129.64   5.175%   $136.3489   $136.35   $136.35   $136.30  
  Purchase #5 $174.71   11.281%   $194.419   $194.42   $194.40   $194.40  
  Purchase #6 $194.47   12.285%   $218.3606   $218.36   $218.35   $218.40  
  Purchase #7 $221.91   6.638%   $236.6404   $236.64   $236.65   $236.60  
  7 purchase totals = $1,011.59       $1,095.8531   $1,095.86   $1,095.80   $1,095.80