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	$39.71	4.575%	$41.5267	$41.53	$41.55	$41.50
Purchase #2	$222.25	13.821%	$252.9672	$252.97	$252.95	$253.00
Purchase #3	$65.70	10.275%	$72.4507	$72.45	$72.45	$72.50
Purchase #4	$51.37	3.772%	$53.3077	$53.31	$53.30	$53.30
Purchase #5	$101.39	10.336%	$111.8697	$111.87	$111.85	$111.90
Purchase #6	$152.57	5.538%	$161.0193	$161.02	$161.00	$161.00
Purchase #7	$79.67	5.140%	$83.765	$83.77	$83.75	$83.80
7 purchase totals =	$712.66		$776.9063	$776.92	$776.85	$777.00