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	$49.58	6.281%	$52.6941	$52.69	$52.70	$52.70
Purchase #2	$105.73	5.429%	$111.4701	$111.47	$111.45	$111.50
Purchase #3	$136.71	5.401%	$144.0937	$144.09	$144.10	$144.10
Purchase #4	$199.57	7.344%	$214.2264	$214.23	$214.25	$214.20
Purchase #5	$141.82	10.456%	$156.6487	$156.65	$156.65	$156.60
Purchase #6	$92.75	6.742%	$99.0032	$99.00	$99.00	$99.00
Purchase #7	$180.74	10.827%	$200.3087	$200.31	$200.30	$200.30
7 purchase totals =	$906.90		$978.4449	$978.44	$978.45	$978.40