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 $249.35   12.807%   $281.2843   $281.28   $281.30   $281.30  
  Purchase #2 $157.33   10.343%   $173.6026   $173.60   $173.60   $173.60  
  Purchase #3 $19.73   6.409%   $20.9945   $20.99   $21.00   $21.00  
  Purchase #4 $59.25   3.556%   $61.3569   $61.36   $61.35   $61.40  
  Purchase #5 $195.35   5.618%   $206.3248   $206.32   $206.30   $206.30  
  Purchase #6 $185.59   6.112%   $196.9333   $196.93   $196.95   $196.90  
  Purchase #7 $203.71   4.794%   $213.4759   $213.48   $213.50   $213.50  
  7 purchase totals = $1,070.31       $1,153.9723   $1,153.96   $1,154.00   $1,154.00