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 $65.66   3.834%   $68.1774   $68.18   $68.20   $68.20  
  Purchase #2 $114.37   9.303%   $125.0098   $125.01   $125.00   $125.00  
  Purchase #3 $186.32   3.305%   $192.4779   $192.48   $192.50   $192.50  
  Purchase #4 $78.74   13.835%   $89.6337   $89.63   $89.65   $89.60  
  Purchase #5 $223.26   10.700%   $247.1488   $247.15   $247.15   $247.10  
  Purchase #6 $195.75   12.596%   $220.4067   $220.41   $220.40   $220.40  
  Purchase #7 $21.65   8.367%   $23.4615   $23.46   $23.45   $23.50  
  7 purchase totals = $885.75       $966.3158   $966.32   $966.35   $966.30