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 $57.66   4.767%   $60.4087   $60.41   $60.40   $60.40  
  Purchase #2 $213.89   10.203%   $235.7132   $235.71   $235.70   $235.70  
  Purchase #3 $184.55   8.327%   $199.9175   $199.92   $199.90   $199.90  
  Purchase #4 $217.37   13.316%   $246.315   $246.32   $246.30   $246.30  
  Purchase #5 $121.25   5.345%   $127.7308   $127.73   $127.75   $127.70  
  Purchase #6 $182.49   9.114%   $199.1221   $199.12   $199.10   $199.10  
  Purchase #7 $34.41   4.782%   $36.0555   $36.06   $36.05   $36.10  
  7 purchase totals = $1,011.62       $1,105.2628   $1,105.27   $1,105.20   $1,105.20