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 $34.95   9.328%   $38.2101   $38.21   $38.20   $38.20  
  Purchase #2 $185.79   12.142%   $208.3486   $208.35   $208.35   $208.30  
  Purchase #3 $70.60   3.430%   $73.0216   $73.02   $73.00   $73.00  
  Purchase #4 $71.44   9.866%   $78.4883   $78.49   $78.50   $78.50  
  Purchase #5 $57.56   12.662%   $64.8482   $64.85   $64.85   $64.80  
  Purchase #6 $239.69   6.803%   $255.9961   $256.00   $256.00   $256.00  
  Purchase #7 $161.56   7.120%   $173.0631   $173.06   $173.05   $173.10  
  7 purchase totals = $821.59       $891.9760   $891.98   $891.95   $891.90