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 $208.86   13.444%   $236.9391   $236.94   $236.95   $236.90  
  Purchase #2 $149.87   9.253%   $163.7375   $163.74   $163.75   $163.70  
  Purchase #3 $181.67   6.408%   $193.3114   $193.31   $193.30   $193.30  
  Purchase #4 $248.93   4.597%   $260.3733   $260.37   $260.35   $260.40  
  Purchase #5 $142.62   8.479%   $154.7127   $154.71   $154.70   $154.70  
  Purchase #6 $249.42   13.169%   $282.2661   $282.27   $282.25   $282.30  
  Purchase #7 $187.43   6.320%   $199.2756   $199.28   $199.30   $199.30  
  7 purchase totals = $1,368.80       $1,490.6157   $1,490.62   $1,490.60   $1,490.60