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 $68.42   7.579%   $73.6056   $73.61   $73.60   $73.60  
  Purchase #2 $85.77   8.750%   $93.2749   $93.27   $93.25   $93.30  
  Purchase #3 $244.79   5.521%   $258.3049   $258.30   $258.30   $258.30  
  Purchase #4 $143.87   10.832%   $159.454   $159.45   $159.45   $159.50  
  Purchase #5 $230.93   8.667%   $250.9447   $250.94   $250.95   $250.90  
  Purchase #6 $139.96   12.527%   $157.4928   $157.49   $157.50   $157.50  
  Purchase #7 $155.55   11.392%   $173.2703   $173.27   $173.25   $173.30  
  7 purchase totals = $1,069.29       $1,166.3472   $1,166.33   $1,166.30   $1,166.40