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 $246.41   5.491%   $259.9404   $259.94   $259.95   $259.90  
  Purchase #2 $83.68   10.677%   $92.6145   $92.61   $92.60   $92.60  
  Purchase #3 $122.34   4.312%   $127.6153   $127.62   $127.60   $127.60  
  Purchase #4 $131.93   6.719%   $140.7944   $140.79   $140.80   $140.80  
  Purchase #5 $73.98   13.545%   $84.0006   $84.00   $84.00   $84.00  
  Purchase #6 $33.98   7.395%   $36.4928   $36.49   $36.50   $36.50  
  Purchase #7 $104.97   6.461%   $111.7521   $111.75   $111.75   $111.80  
  7 purchase totals = $797.29       $853.2101   $853.20   $853.20   $853.20