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	$47.86	13.738%	$54.435	$54.44	$54.45	$54.40
Purchase #2	$49.42	10.332%	$54.5261	$54.53	$54.55	$54.50
Purchase #3	$203.46	6.794%	$217.2831	$217.28	$217.30	$217.30
Purchase #4	$124.50	5.436%	$131.2678	$131.27	$131.25	$131.30
Purchase #5	$6.82	3.656%	$7.0693	$7.07	$7.05	$7.10
Purchase #6	$175.44	9.830%	$192.6858	$192.69	$192.70	$192.70
Purchase #7	$166.95	3.587%	$172.9385	$172.94	$172.95	$172.90
7 purchase totals =	$774.45		$830.2056	$830.22	$830.25	$830.20