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 $57.34   8.454%   $62.1875   $62.19   $62.20   $62.20  
  Purchase #2 $222.40   6.164%   $236.1087   $236.11   $236.10   $236.10  
  Purchase #3 $134.30   7.493%   $144.3631   $144.36   $144.35   $144.40  
  Purchase #4 $157.67   10.335%   $173.9652   $173.97   $173.95   $174.00  
  Purchase #5 $176.77   10.457%   $195.2548   $195.25   $195.25   $195.30  
  Purchase #6 $77.41   12.840%   $87.3494   $87.35   $87.35   $87.30  
  Purchase #7 $227.88   7.635%   $245.2786   $245.28   $245.30   $245.30  
  7 purchase totals = $1,053.77       $1,144.5073   $1,144.51   $1,144.50   $1,144.60