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 $64.99   13.302%   $73.635   $73.64   $73.65   $73.60  
  Purchase #2 $30.89   9.388%   $33.79   $33.79   $33.80   $33.80  
  Purchase #3 $221.93   11.539%   $247.5385   $247.54   $247.55   $247.50  
  Purchase #4 $210.62   6.321%   $223.9333   $223.93   $223.95   $223.90  
  Purchase #5 $108.70   13.314%   $123.1723   $123.17   $123.15   $123.20  
  Purchase #6 $88.91   6.549%   $94.7327   $94.73   $94.75   $94.70  
  Purchase #7 $249.43   10.764%   $276.2786   $276.28   $276.30   $276.30  
  7 purchase totals = $975.47       $1,073.0804   $1,073.08   $1,073.15   $1,073.00