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 $118.82   6.394%   $126.4174   $126.42   $126.40   $126.40  
  Purchase #2 $181.47   8.707%   $197.2706   $197.27   $197.25   $197.30  
  Purchase #3 $97.99   4.307%   $102.2104   $102.21   $102.20   $102.20  
  Purchase #4 $208.84   5.634%   $220.606   $220.61   $220.60   $220.60  
  Purchase #5 $219.94   7.831%   $237.1635   $237.16   $237.15   $237.20  
  Purchase #6 $196.35   8.559%   $213.1556   $213.16   $213.15   $213.20  
  Purchase #7 $239.43   4.711%   $250.7095   $250.71   $250.70   $250.70  
  7 purchase totals = $1,262.84       $1,347.5330   $1,347.54   $1,347.45   $1,347.60