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 $67.47   3.538%   $69.8571   $69.86   $69.85   $69.90  
  Purchase #2 $53.44   5.385%   $56.3177   $56.32   $56.30   $56.30  
  Purchase #3 $214.93   13.569%   $244.0939   $244.09   $244.10   $244.10  
  Purchase #4 $148.59   12.543%   $167.2276   $167.23   $167.25   $167.20  
  Purchase #5 $112.67   10.201%   $124.1635   $124.16   $124.15   $124.20  
  Purchase #6 $106.65   10.597%   $117.9517   $117.95   $117.95   $118.00  
  Purchase #7 $225.98   8.247%   $244.6166   $244.62   $244.60   $244.60  
  7 purchase totals = $929.73       $1,024.2281   $1,024.23   $1,024.20   $1,024.30