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 $191.26   11.730%   $213.6948   $213.69   $213.70   $213.70  
  Purchase #2 $222.31   6.569%   $236.9135   $236.91   $236.90   $236.90  
  Purchase #3 $95.43   13.634%   $108.4409   $108.44   $108.45   $108.40  
  Purchase #4 $149.98   8.741%   $163.0898   $163.09   $163.10   $163.10  
  Purchase #5 $112.50   3.293%   $116.2046   $116.20   $116.20   $116.20  
  Purchase #6 $223.63   4.464%   $233.6128   $233.61   $233.60   $233.60  
  Purchase #7 $117.75   11.732%   $131.5644   $131.56   $131.55   $131.60  
  7 purchase totals = $1,112.86       $1,203.5208   $1,203.50   $1,203.50   $1,203.50