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 $167.32   10.574%   $185.0124   $185.01   $185.00   $185.00  
  Purchase #2 $129.39   10.235%   $142.6331   $142.63   $142.65   $142.60  
  Purchase #3 $198.78   8.155%   $214.9905   $214.99   $215.00   $215.00  
  Purchase #4 $12.25   8.693%   $13.3149   $13.31   $13.30   $13.30  
  Purchase #5 $216.65   9.155%   $236.4843   $236.48   $236.50   $236.50  
  Purchase #6 $184.73   8.738%   $200.8717   $200.87   $200.85   $200.90  
  Purchase #7 $73.39   13.299%   $83.1501   $83.15   $83.15   $83.20  
  7 purchase totals = $982.51       $1,076.4570   $1,076.44   $1,076.45   $1,076.50