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 $246.59   6.496%   $262.6085   $262.61   $262.60   $262.60  
  Purchase #2 $112.48   11.378%   $125.278   $125.28   $125.30   $125.30  
  Purchase #3 $118.81   13.147%   $134.43   $134.43   $134.45   $134.40  
  Purchase #4 $184.54   10.444%   $203.8134   $203.81   $203.80   $203.80  
  Purchase #5 $158.43   6.605%   $168.8943   $168.89   $168.90   $168.90  
  Purchase #6 $165.92   6.481%   $176.6733   $176.67   $176.65   $176.70  
  Purchase #7 $248.27   9.750%   $272.4763   $272.48   $272.50   $272.50  
  7 purchase totals = $1,235.04       $1,344.1738   $1,344.17   $1,344.20   $1,344.20