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 $246.30   9.232%   $269.0384   $269.04   $269.05   $269.00  
  Purchase #2 $151.69   12.859%   $171.1958   $171.20   $171.20   $171.20  
  Purchase #3 $59.58   8.726%   $64.779   $64.78   $64.80   $64.80  
  Purchase #4 $60.50   9.788%   $66.4217   $66.42   $66.40   $66.40  
  Purchase #5 $170.99   3.268%   $176.578   $176.58   $176.60   $176.60  
  Purchase #6 $163.82   5.659%   $173.0906   $173.09   $173.10   $173.10  
  Purchase #7 $218.25   9.571%   $239.1387   $239.14   $239.15   $239.10  
  7 purchase totals = $1,071.13       $1,160.2422   $1,160.25   $1,160.30   $1,160.20