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 $157.25   10.268%   $173.3964   $173.40   $173.40   $173.40  
  Purchase #2 $188.90   13.567%   $214.5281   $214.53   $214.55   $214.50  
  Purchase #3 $215.78   12.554%   $242.869   $242.87   $242.85   $242.90  
  Purchase #4 $12.84   9.366%   $14.0426   $14.04   $14.05   $14.00  
  Purchase #5 $212.56   3.599%   $220.21   $220.21   $220.20   $220.20  
  Purchase #6 $152.53   11.339%   $169.8254   $169.83   $169.85   $169.80  
  Purchase #7 $208.98   5.471%   $220.4133   $220.41   $220.40   $220.40  
  7 purchase totals = $1,148.84       $1,255.2848   $1,255.29   $1,255.30   $1,255.20