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	$169.75	6.257%	$180.3713	$180.37	$180.35	$180.40
Purchase #2	$79.99	3.336%	$82.6585	$82.66	$82.65	$82.70
Purchase #3	$37.36	9.527%	$40.9193	$40.92	$40.90	$40.90
Purchase #4	$134.27	10.379%	$148.2059	$148.21	$148.20	$148.20
Purchase #5	$106.82	4.600%	$111.7337	$111.73	$111.75	$111.70
Purchase #6	$187.65	4.568%	$196.2219	$196.22	$196.20	$196.20
Purchase #7	$58.87	11.615%	$65.7078	$65.71	$65.70	$65.70
7 purchase totals =	$774.71		$825.8184	$825.82	$825.75	$825.80