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 $33.40   13.555%   $37.9274   $37.93   $37.95   $37.90  
  Purchase #2 $42.33   13.567%   $48.0729   $48.07   $48.05   $48.10  
  Purchase #3 $114.84   13.559%   $130.4112   $130.41   $130.40   $130.40  
  Purchase #4 $66.82   5.391%   $70.4223   $70.42   $70.40   $70.40  
  Purchase #5 $249.97   13.201%   $282.9685   $282.97   $282.95   $283.00  
  Purchase #6 $58.25   5.631%   $61.5301   $61.53   $61.55   $61.50  
  Purchase #7 $55.87   7.331%   $59.9658   $59.97   $59.95   $60.00  
  7 purchase totals = $621.48       $691.2982   $691.30   $691.25   $691.30