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 $235.99   4.367%   $246.2957   $246.30   $246.30   $246.30  
  Purchase #2 $109.79   4.389%   $114.6087   $114.61   $114.60   $114.60  
  Purchase #3 $42.28   10.237%   $46.6082   $46.61   $46.60   $46.60  
  Purchase #4 $119.75   9.465%   $131.0843   $131.08   $131.10   $131.10  
  Purchase #5 $11.47   7.356%   $12.3137   $12.31   $12.30   $12.30  
  Purchase #6 $121.37   12.523%   $136.5692   $136.57   $136.55   $136.60  
  Purchase #7 $166.62   10.156%   $183.5419   $183.54   $183.55   $183.50  
  7 purchase totals = $807.27       $871.0217   $871.02   $871.00   $871.00