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	$14.36	10.626%	$15.8859	$15.89	$15.90	$15.90
Purchase #2	$118.33	10.854%	$131.1735	$131.17	$131.15	$131.20
Purchase #3	$25.46	6.730%	$27.1735	$27.17	$27.15	$27.20
Purchase #4	$5.95	10.105%	$6.5512	$6.55	$6.55	$6.60
Purchase #5	$205.99	4.801%	$215.8796	$215.88	$215.90	$215.90
Purchase #6	$47.33	4.769%	$49.5872	$49.59	$49.60	$49.60
Purchase #7	$87.71	4.652%	$91.7903	$91.79	$91.80	$91.80
7 purchase totals =	$505.13		$538.0412	$538.04	$538.05	$538.20