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 $206.76   8.636%   $224.6158   $224.62   $224.60   $224.60  
  Purchase #2 $105.33   3.126%   $108.6226   $108.62   $108.60   $108.60  
  Purchase #3 $215.94   7.852%   $232.8956   $232.90   $232.90   $232.90  
  Purchase #4 $168.92   4.531%   $176.5738   $176.57   $176.55   $176.60  
  Purchase #5 $158.36   10.316%   $174.6964   $174.70   $174.70   $174.70  
  Purchase #6 $63.78   13.427%   $72.3437   $72.34   $72.35   $72.30  
  Purchase #7 $192.92   9.371%   $210.9985   $211.00   $211.00   $211.00  
  7 purchase totals = $1,112.01       $1,200.7464   $1,200.75   $1,200.70   $1,200.70