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 $159.55   10.463%   $176.2437   $176.24   $176.25   $176.20  
  Purchase #2 $54.53   4.258%   $56.8519   $56.85   $56.85   $56.90  
  Purchase #3 $81.55   3.701%   $84.5682   $84.57   $84.55   $84.60  
  Purchase #4 $98.92   9.112%   $107.9336   $107.93   $107.95   $107.90  
  Purchase #5 $191.43   12.268%   $214.9146   $214.91   $214.90   $214.90  
  Purchase #6 $73.34   5.358%   $77.2696   $77.27   $77.25   $77.30  
  Purchase #7 $188.53   3.601%   $195.319   $195.32   $195.30   $195.30  
  7 purchase totals = $847.85       $913.1006   $913.09   $913.05   $913.10