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 $248.55   5.373%   $261.9046   $261.90   $261.90   $261.90  
  Purchase #2 $6.46   6.851%   $6.9026   $6.90   $6.90   $6.90  
  Purchase #3 $93.65   11.326%   $104.2568   $104.26   $104.25   $104.30  
  Purchase #4 $113.25   13.159%   $128.1526   $128.15   $128.15   $128.20  
  Purchase #5 $84.87   6.536%   $90.4171   $90.42   $90.40   $90.40  
  Purchase #6 $205.98   4.757%   $215.7785   $215.78   $215.80   $215.80  
  Purchase #7 $202.26   3.701%   $209.7456   $209.75   $209.75   $209.70  
  7 purchase totals = $955.02       $1,017.1578   $1,017.16   $1,017.15   $1,017.20