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	$233.71	13.872%	$266.1303	$266.13	$266.15	$266.10
Purchase #2	$92.79	11.349%	$103.3207	$103.32	$103.30	$103.30
Purchase #3	$172.95	13.688%	$196.6234	$196.62	$196.60	$196.60
Purchase #4	$209.76	13.542%	$238.1657	$238.17	$238.15	$238.20
Purchase #5	$5.27	12.667%	$5.9376	$5.94	$5.95	$5.90
Purchase #6	$172.64	10.221%	$190.2855	$190.29	$190.30	$190.30
Purchase #7	$187.27	8.453%	$203.0999	$203.10	$203.10	$203.10
7 purchase totals =	$1,074.39		$1,203.5631	$1,203.57	$1,203.55	$1,203.50