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	$93.85	7.530%	$100.9169	$100.92	$100.90	$100.90
Purchase #2	$221.65	10.526%	$244.9809	$244.98	$245.00	$245.00
Purchase #3	$197.87	6.178%	$210.0944	$210.09	$210.10	$210.10
Purchase #4	$160.82	7.751%	$173.2852	$173.29	$173.30	$173.30
Purchase #5	$12.36	4.617%	$12.9307	$12.93	$12.95	$12.90
Purchase #6	$112.68	13.812%	$128.2434	$128.24	$128.25	$128.20
Purchase #7	$142.89	3.472%	$147.8511	$147.85	$147.85	$147.90
7 purchase totals =	$942.12		$1,018.3026	$1,018.30	$1,018.35	$1,018.30