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 $208.86   3.213%   $215.5707   $215.57   $215.55   $215.60  
  Purchase #2 $56.79   9.664%   $62.2782   $62.28   $62.30   $62.30  
  Purchase #3 $18.68   5.677%   $19.7405   $19.74   $19.75   $19.70  
  Purchase #4 $238.45   7.167%   $255.5397   $255.54   $255.55   $255.50  
  Purchase #5 $227.66   5.277%   $239.6736   $239.67   $239.65   $239.70  
  Purchase #6 $85.25   11.404%   $94.9719   $94.97   $94.95   $95.00  
  Purchase #7 $218.32   4.226%   $227.5462   $227.55   $227.55   $227.50  
  7 purchase totals = $1,054.01       $1,115.3208   $1,115.32   $1,115.30   $1,115.30