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	$220.80	3.384%	$228.2719	$228.27	$228.25	$228.30
Purchase #2	$45.41	11.614%	$50.6839	$50.68	$50.70	$50.70
Purchase #3	$226.41	12.162%	$253.946	$253.95	$253.95	$253.90
Purchase #4	$49.82	3.810%	$51.7181	$51.72	$51.70	$51.70
Purchase #5	$93.33	13.268%	$105.713	$105.71	$105.70	$105.70
Purchase #6	$30.74	7.659%	$33.0944	$33.09	$33.10	$33.10
Purchase #7	$99.38	12.558%	$111.8601	$111.86	$111.85	$111.90
7 purchase totals =	$765.89		$835.2874	$835.28	$835.25	$835.30