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 $121.51   3.823%   $126.1553   $126.16   $126.15   $126.20  
  Purchase #2 $173.66   5.303%   $182.8692   $182.87   $182.85   $182.90  
  Purchase #3 $208.73   7.136%   $223.625   $223.63   $223.65   $223.60  
  Purchase #4 $211.25   8.722%   $229.6752   $229.68   $229.70   $229.70  
  Purchase #5 $160.99   9.739%   $176.6688   $176.67   $176.65   $176.70  
  Purchase #6 $138.26   6.443%   $147.1681   $147.17   $147.15   $147.20  
  Purchase #7 $13.88   11.874%   $15.5281   $15.53   $15.55   $15.50  
  7 purchase totals = $1,028.28       $1,101.6897   $1,101.71   $1,101.70   $1,101.80