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 $206.34   4.212%   $215.031   $215.03   $215.05   $215.00  
  Purchase #2 $35.77   8.367%   $38.7629   $38.76   $38.75   $38.80  
  Purchase #3 $85.79   11.553%   $95.7013   $95.70   $95.70   $95.70  
  Purchase #4 $237.31   12.377%   $266.6819   $266.68   $266.70   $266.70  
  Purchase #5 $230.31   8.111%   $248.9904   $248.99   $249.00   $249.00  
  Purchase #6 $223.62   6.384%   $237.8959   $237.90   $237.90   $237.90  
  Purchase #7 $60.80   10.767%   $67.3463   $67.35   $67.35   $67.30  
  7 purchase totals = $1,079.94       $1,170.4097   $1,170.41   $1,170.45   $1,170.40