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	$101.49	10.272%	$111.9151	$111.92	$111.90	$111.90
Purchase #2	$31.32	12.307%	$35.1746	$35.17	$35.15	$35.20
Purchase #3	$140.30	4.370%	$146.4311	$146.43	$146.45	$146.40
Purchase #4	$98.58	11.814%	$110.2262	$110.23	$110.25	$110.20
Purchase #5	$20.62	11.177%	$22.9247	$22.92	$22.90	$22.90
Purchase #6	$238.91	12.126%	$267.8802	$267.88	$267.90	$267.90
Purchase #7	$94.52	13.300%	$107.0912	$107.09	$107.10	$107.10
7 purchase totals =	$725.74		$801.6431	$801.64	$801.65	$801.60