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 $236.67   4.183%   $246.5699   $246.57   $246.55   $246.60  
  Purchase #2 $63.48   11.557%   $70.8164   $70.82   $70.80   $70.80  
  Purchase #3 $185.98   11.763%   $207.8568   $207.86   $207.85   $207.90  
  Purchase #4 $121.46   4.357%   $126.752   $126.75   $126.75   $126.80  
  Purchase #5 $186.40   11.361%   $207.5769   $207.58   $207.60   $207.60  
  Purchase #6 $245.99   12.102%   $275.7597   $275.76   $275.75   $275.80  
  Purchase #7 $12.89   10.634%   $14.2607   $14.26   $14.25   $14.30  
  7 purchase totals = $1,052.87       $1,149.5924   $1,149.60   $1,149.55   $1,149.80