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 $214.51   10.154%   $236.2913   $236.29   $236.30   $236.30  
  Purchase #2 $121.92   7.723%   $131.3359   $131.34   $131.35   $131.30  
  Purchase #3 $173.25   8.300%   $187.6298   $187.63   $187.65   $187.60  
  Purchase #4 $58.42   11.729%   $65.2721   $65.27   $65.25   $65.30  
  Purchase #5 $118.69   13.307%   $134.4841   $134.48   $134.50   $134.50  
  Purchase #6 $190.96   13.805%   $217.322   $217.32   $217.30   $217.30  
  Purchase #7 $188.32   13.581%   $213.8957   $213.90   $213.90   $213.90  
  7 purchase totals = $1,066.07       $1,186.2309   $1,186.23   $1,186.25   $1,186.20