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	$238.70	13.668%	$271.3255	$271.33	$271.35	$271.30
Purchase #2	$9.56	11.332%	$10.6433	$10.64	$10.65	$10.60
Purchase #3	$37.49	5.545%	$39.5688	$39.57	$39.55	$39.60
Purchase #4	$91.66	10.850%	$101.6051	$101.61	$101.60	$101.60
Purchase #5	$10.35	4.276%	$10.7926	$10.79	$10.80	$10.80
Purchase #6	$154.46	5.441%	$162.8642	$162.86	$162.85	$162.90
Purchase #7	$89.35	3.550%	$92.5219	$92.52	$92.50	$92.50
7 purchase totals =	$631.57		$689.3214	$689.32	$689.30	$689.30