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 $114.77   6.631%   $122.3804   $122.38   $122.40   $122.40  
  Purchase #2 $248.73   13.752%   $282.9353   $282.94   $282.95   $282.90  
  Purchase #3 $158.28   9.854%   $173.8769   $173.88   $173.90   $173.90  
  Purchase #4 $181.92   10.630%   $201.2581   $201.26   $201.25   $201.30  
  Purchase #5 $5.45   7.283%   $5.8469   $5.85   $5.85   $5.80  
  Purchase #6 $205.41   11.642%   $229.3238   $229.32   $229.30   $229.30  
  Purchase #7 $118.83   11.208%   $132.1485   $132.15   $132.15   $132.10  
  7 purchase totals = $1,033.39       $1,147.7699   $1,147.78   $1,147.80   $1,147.70