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 $5.30   3.534%   $5.4873   $5.49   $5.50   $5.50  
  Purchase #2 $215.56   5.783%   $228.0258   $228.03   $228.05   $228.00  
  Purchase #3 $232.78   12.476%   $261.8216   $261.82   $261.80   $261.80  
  Purchase #4 $40.58   11.382%   $45.1988   $45.20   $45.20   $45.20  
  Purchase #5 $21.94   10.405%   $24.2229   $24.22   $24.20   $24.20  
  Purchase #6 $100.26   7.176%   $107.4547   $107.45   $107.45   $107.50  
  Purchase #7 $214.30   13.312%   $242.8276   $242.83   $242.85   $242.80  
  7 purchase totals = $830.72       $915.0387   $915.04   $915.05   $915.00