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 $43.45   6.294%   $46.1847   $46.18   $46.20   $46.20  
  Purchase #2 $121.32   13.491%   $137.6873   $137.69   $137.70   $137.70  
  Purchase #3 $119.49   6.115%   $126.7968   $126.80   $126.80   $126.80  
  Purchase #4 $227.83   5.728%   $240.8801   $240.88   $240.90   $240.90  
  Purchase #5 $122.41   12.699%   $137.9548   $137.95   $137.95   $138.00  
  Purchase #6 $79.61   5.394%   $83.9042   $83.90   $83.90   $83.90  
  Purchase #7 $187.37   3.321%   $193.5926   $193.59   $193.60   $193.60  
  7 purchase totals = $901.48       $967.0005   $966.99   $967.05   $967.10