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	$137.53	13.656%	$156.3111	$156.31	$156.30	$156.30
Purchase #2	$230.80	10.572%	$255.2002	$255.20	$255.20	$255.20
Purchase #3	$99.64	11.661%	$111.259	$111.26	$111.25	$111.30
Purchase #4	$106.88	10.116%	$117.692	$117.69	$117.70	$117.70
Purchase #5	$208.33	8.313%	$225.6485	$225.65	$225.65	$225.60
Purchase #6	$236.53	8.194%	$255.9113	$255.91	$255.90	$255.90
Purchase #7	$71.46	10.162%	$78.7218	$78.72	$78.70	$78.70
7 purchase totals =	$1,091.17		$1,200.7439	$1,200.74	$1,200.70	$1,200.70