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 $192.25   11.258%   $213.8935   $213.89   $213.90   $213.90  
  Purchase #2 $96.30   8.193%   $104.1899   $104.19   $104.20   $104.20  
  Purchase #3 $84.72   7.769%   $91.3019   $91.30   $91.30   $91.30  
  Purchase #4 $224.64   9.786%   $246.6233   $246.62   $246.60   $246.60  
  Purchase #5 $111.66   11.555%   $124.5623   $124.56   $124.55   $124.60  
  Purchase #6 $123.27   6.234%   $130.9547   $130.95   $130.95   $131.00  
  Purchase #7 $152.61   3.672%   $158.2138   $158.21   $158.20   $158.20  
  7 purchase totals = $985.45       $1,069.7394   $1,069.72   $1,069.70   $1,069.80