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 $228.54   6.558%   $243.5277   $243.53   $243.55   $243.50  
  Purchase #2 $125.45   13.130%   $141.9216   $141.92   $141.90   $141.90  
  Purchase #3 $236.58   9.612%   $259.3201   $259.32   $259.30   $259.30  
  Purchase #4 $61.79   7.311%   $66.3075   $66.31   $66.30   $66.30  
  Purchase #5 $103.77   9.861%   $114.0028   $114.00   $114.00   $114.00  
  Purchase #6 $230.37   13.440%   $261.3317   $261.33   $261.35   $261.30  
  Purchase #7 $158.68   3.259%   $163.8514   $163.85   $163.85   $163.90  
  7 purchase totals = $1,145.18       $1,250.2628   $1,250.26   $1,250.25   $1,250.20