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 $42.63   10.722%   $47.2008   $47.20   $47.20   $47.20  
  Purchase #2 $110.44   4.511%   $115.4219   $115.42   $115.40   $115.40  
  Purchase #3 $36.46   3.230%   $37.6377   $37.64   $37.65   $37.60  
  Purchase #4 $245.82   5.315%   $258.8853   $258.89   $258.90   $258.90  
  Purchase #5 $238.56   9.766%   $261.8578   $261.86   $261.85   $261.90  
  Purchase #6 $240.92   5.393%   $253.9128   $253.91   $253.90   $253.90  
  Purchase #7 $23.58   8.608%   $25.6098   $25.61   $25.60   $25.60  
  7 purchase totals = $938.41       $1,000.5261   $1,000.53   $1,000.50   $1,000.50