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	$172.46	4.305%	$179.8844	$179.88	$179.90	$179.90
Purchase #2	$172.55	8.555%	$187.3117	$187.31	$187.30	$187.30
Purchase #3	$50.39	10.261%	$55.5605	$55.56	$55.55	$55.60
Purchase #4	$69.95	11.493%	$77.9894	$77.99	$78.00	$78.00
Purchase #5	$238.44	3.776%	$247.4435	$247.44	$247.45	$247.40
Purchase #6	$44.27	12.298%	$49.7143	$49.71	$49.70	$49.70
Purchase #7	$64.30	12.654%	$72.4365	$72.44	$72.45	$72.40
7 purchase totals =	$812.36		$870.3403	$870.33	$870.35	$870.30