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 $24.62   4.479%   $25.7227   $25.72   $25.70   $25.70  
  Purchase #2 $194.95   6.816%   $208.2378   $208.24   $208.25   $208.20  
  Purchase #3 $130.44   10.125%   $143.6471   $143.65   $143.65   $143.60  
  Purchase #4 $227.63   10.122%   $250.6707   $250.67   $250.65   $250.70  
  Purchase #5 $79.60   9.207%   $86.9288   $86.93   $86.95   $86.90  
  Purchase #6 $24.74   3.198%   $25.5312   $25.53   $25.55   $25.50  
  Purchase #7 $173.84   7.342%   $186.6033   $186.60   $186.60   $186.60  
  7 purchase totals = $855.82       $927.3416   $927.34   $927.35   $927.20