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	$170.66	6.333%	$181.4679	$181.47	$181.45	$181.50
Purchase #2	$70.95	8.860%	$77.2362	$77.24	$77.25	$77.20
Purchase #3	$47.26	9.840%	$51.9104	$51.91	$51.90	$51.90
Purchase #4	$48.68	3.370%	$50.3205	$50.32	$50.30	$50.30
Purchase #5	$206.84	7.388%	$222.1213	$222.12	$222.10	$222.10
Purchase #6	$79.36	12.699%	$89.4379	$89.44	$89.45	$89.40
Purchase #7	$53.41	5.267%	$56.2231	$56.22	$56.20	$56.20
7 purchase totals =	$677.16		$728.7173	$728.72	$728.65	$728.60