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	$158.51	12.141%	$177.7547	$177.75	$177.75	$177.80
Purchase #2	$141.85	6.749%	$151.4235	$151.42	$151.40	$151.40
Purchase #3	$208.63	5.232%	$219.5455	$219.55	$219.55	$219.50
Purchase #4	$49.48	13.647%	$56.2325	$56.23	$56.25	$56.20
Purchase #5	$84.72	6.211%	$89.982	$89.98	$90.00	$90.00
Purchase #6	$129.56	11.656%	$144.6615	$144.66	$144.65	$144.70
Purchase #7	$73.46	12.608%	$82.7218	$82.72	$82.70	$82.70
7 purchase totals =	$846.21		$922.3215	$922.31	$922.30	$922.30