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 $241.61   11.588%   $269.6078   $269.61   $269.60   $269.60  
  Purchase #2 $190.35   7.238%   $204.1275   $204.13   $204.15   $204.10  
  Purchase #3 $137.74   12.467%   $154.912   $154.91   $154.90   $154.90  
  Purchase #4 $159.67   12.295%   $179.3014   $179.30   $179.30   $179.30  
  Purchase #5 $213.93   6.669%   $228.197   $228.20   $228.20   $228.20  
  Purchase #6 $119.26   5.724%   $126.0864   $126.09   $126.10   $126.10  
  Purchase #7 $16.66   10.484%   $18.4066   $18.41   $18.40   $18.40  
  7 purchase totals = $1,079.22       $1,180.6387   $1,180.65   $1,180.65   $1,180.60