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 $187.81   6.329%   $199.6965   $199.70   $199.70   $199.70  
  Purchase #2 $125.47   8.832%   $136.5515   $136.55   $136.55   $136.60  
  Purchase #3 $137.75   8.159%   $148.989   $148.99   $149.00   $149.00  
  Purchase #4 $193.70   11.518%   $216.0104   $216.01   $216.00   $216.00  
  Purchase #5 $32.37   9.103%   $35.3166   $35.32   $35.30   $35.30  
  Purchase #6 $42.32   10.840%   $46.9075   $46.91   $46.90   $46.90  
  Purchase #7 $68.29   5.382%   $71.9654   $71.97   $71.95   $72.00  
  7 purchase totals = $787.71       $855.4369   $855.45   $855.40   $855.50