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 $35.88   5.412%   $37.8218   $37.82   $37.80   $37.80  
  Purchase #2 $106.34   8.117%   $114.9716   $114.97   $114.95   $115.00  
  Purchase #3 $17.25   5.644%   $18.2236   $18.22   $18.20   $18.20  
  Purchase #4 $64.60   7.440%   $69.4062   $69.41   $69.40   $69.40  
  Purchase #5 $176.58   5.158%   $185.688   $185.69   $185.70   $185.70  
  Purchase #6 $165.48   4.706%   $173.2675   $173.27   $173.25   $173.30  
  Purchase #7 $167.65   9.566%   $183.6874   $183.69   $183.70   $183.70  
  7 purchase totals = $733.78       $783.0661   $783.07   $783.00   $783.10