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 $145.62   13.499%   $165.2772   $165.28   $165.30   $165.30  
  Purchase #2 $66.27   7.141%   $71.0023   $71.00   $71.00   $71.00  
  Purchase #3 $185.48   5.499%   $195.6795   $195.68   $195.70   $195.70  
  Purchase #4 $203.89   6.196%   $216.523   $216.52   $216.50   $216.50  
  Purchase #5 $87.87   8.293%   $95.1571   $95.16   $95.15   $95.20  
  Purchase #6 $183.50   4.775%   $192.2621   $192.26   $192.25   $192.30  
  Purchase #7 $44.85   8.146%   $48.5035   $48.50   $48.50   $48.50  
  7 purchase totals = $917.48       $984.4047   $984.40   $984.40   $984.50