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 $56.77   6.186%   $60.2818   $60.28   $60.30   $60.30  
  Purchase #2 $68.38   12.215%   $76.7326   $76.73   $76.75   $76.70  
  Purchase #3 $96.86   5.539%   $102.2251   $102.23   $102.25   $102.20  
  Purchase #4 $157.85   11.765%   $176.4211   $176.42   $176.40   $176.40  
  Purchase #5 $118.67   12.716%   $133.7601   $133.76   $133.75   $133.80  
  Purchase #6 $208.41   11.374%   $232.1146   $232.11   $232.10   $232.10  
  Purchase #7 $233.77   3.311%   $241.5101   $241.51   $241.50   $241.50  
  7 purchase totals = $940.71       $1,023.0454   $1,023.04   $1,023.05   $1,023.00