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 $118.88   6.829%   $126.9983   $127.00   $127.00   $127.00  
  Purchase #2 $207.66   4.309%   $216.6081   $216.61   $216.60   $216.60  
  Purchase #3 $143.39   7.389%   $153.9851   $153.99   $154.00   $154.00  
  Purchase #4 $46.92   9.827%   $51.5308   $51.53   $51.55   $51.50  
  Purchase #5 $73.85   13.176%   $83.5805   $83.58   $83.60   $83.60  
  Purchase #6 $68.40   8.572%   $74.2632   $74.26   $74.25   $74.30  
  Purchase #7 $93.96   5.149%   $98.798   $98.80   $98.80   $98.80  
  7 purchase totals = $753.06       $805.7640   $805.77   $805.80   $805.80