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	$242.92	6.321%	$258.275	$258.28	$258.30	$258.30
Purchase #2	$68.56	5.619%	$72.4124	$72.41	$72.40	$72.40
Purchase #3	$107.68	8.556%	$116.8931	$116.89	$116.90	$116.90
Purchase #4	$247.43	3.291%	$255.5729	$255.57	$255.55	$255.60
Purchase #5	$71.75	8.107%	$77.5668	$77.57	$77.55	$77.60
Purchase #6	$53.36	5.657%	$56.3786	$56.38	$56.40	$56.40
Purchase #7	$64.84	9.415%	$70.9447	$70.94	$70.95	$70.90
7 purchase totals =	$856.54		$908.0435	$908.04	$908.05	$908.10