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 $185.86   12.303%   $208.7264   $208.73   $208.75   $208.70  
  Purchase #2 $220.37   12.681%   $248.3151   $248.32   $248.30   $248.30  
  Purchase #3 $211.39   7.339%   $226.9039   $226.90   $226.90   $226.90  
  Purchase #4 $247.30   5.111%   $259.9395   $259.94   $259.95   $259.90  
  Purchase #5 $211.28   11.676%   $235.9491   $235.95   $235.95   $235.90  
  Purchase #6 $65.52   4.704%   $68.6021   $68.60   $68.60   $68.60  
  Purchase #7 $179.61   7.594%   $193.2496   $193.25   $193.25   $193.20  
  7 purchase totals = $1,321.33       $1,441.6857   $1,441.69   $1,441.70   $1,441.50