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	$183.88	7.804%	$198.23	$198.23	$198.25	$198.20
Purchase #2	$54.68	4.287%	$57.0241	$57.02	$57.00	$57.00
Purchase #3	$75.29	5.495%	$79.4272	$79.43	$79.45	$79.40
Purchase #4	$165.31	12.468%	$185.9209	$185.92	$185.90	$185.90
Purchase #5	$166.90	3.579%	$172.8734	$172.87	$172.85	$172.90
Purchase #6	$83.32	13.488%	$94.5582	$94.56	$94.55	$94.60
Purchase #7	$47.65	8.579%	$51.7379	$51.74	$51.75	$51.70
7 purchase totals =	$777.03		$839.7717	$839.77	$839.75	$839.70