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 $56.95   13.704%   $64.7544   $64.75   $64.75   $64.80  
  Purchase #2 $214.89   11.443%   $239.4799   $239.48   $239.50   $239.50  
  Purchase #3 $23.97   11.358%   $26.6925   $26.69   $26.70   $26.70  
  Purchase #4 $82.78   9.777%   $90.8734   $90.87   $90.85   $90.90  
  Purchase #5 $42.54   11.178%   $47.2951   $47.30   $47.30   $47.30  
  Purchase #6 $117.74   5.569%   $124.2969   $124.30   $124.30   $124.30  
  Purchase #7 $166.40   6.120%   $176.5837   $176.58   $176.60   $176.60  
  7 purchase totals = $705.27       $769.9759   $769.97   $770.00   $770.10