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 $169.84   13.412%   $192.6189   $192.62   $192.60   $192.60  
  Purchase #2 $32.64   6.543%   $34.7756   $34.78   $34.80   $34.80  
  Purchase #3 $155.25   13.757%   $176.6077   $176.61   $176.60   $176.60  
  Purchase #4 $70.45   6.862%   $75.2843   $75.28   $75.30   $75.30  
  Purchase #5 $50.95   8.445%   $55.2527   $55.25   $55.25   $55.30  
  Purchase #6 $25.62   13.177%   $28.9959   $29.00   $29.00   $29.00  
  Purchase #7 $17.88   7.549%   $19.2298   $19.23   $19.25   $19.20  
  7 purchase totals = $522.63       $582.7649   $582.77   $582.80   $582.80