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 $110.73   13.828%   $126.0417   $126.04   $126.05   $126.00  
  Purchase #2 $209.44   8.851%   $227.9775   $227.98   $228.00   $228.00  
  Purchase #3 $190.95   12.361%   $214.5533   $214.55   $214.55   $214.60  
  Purchase #4 $195.53   6.586%   $208.4076   $208.41   $208.40   $208.40  
  Purchase #5 $216.35   11.473%   $241.1718   $241.17   $241.15   $241.20  
  Purchase #6 $126.36   5.129%   $132.841   $132.84   $132.85   $132.80  
  Purchase #7 $136.93   10.383%   $151.1474   $151.15   $151.15   $151.10  
  7 purchase totals = $1,186.29       $1,302.1403   $1,302.14   $1,302.15   $1,302.10