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	$166.98	10.235%	$184.0704	$184.07	$184.05	$184.10
Purchase #2	$54.90	13.632%	$62.384	$62.38	$62.40	$62.40
Purchase #3	$10.52	6.606%	$11.215	$11.22	$11.20	$11.20
Purchase #4	$58.97	10.490%	$65.156	$65.16	$65.15	$65.20
Purchase #5	$142.36	3.593%	$147.475	$147.48	$147.50	$147.50
Purchase #6	$64.52	9.784%	$70.8326	$70.83	$70.85	$70.80
Purchase #7	$93.37	10.448%	$103.1253	$103.13	$103.15	$103.10
7 purchase totals =	$591.62		$644.2583	$644.27	$644.30	$644.30