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	$28.96	9.142%	$31.6075	$31.61	$31.60	$31.60
Purchase #2	$239.27	5.767%	$253.0687	$253.07	$253.05	$253.10
Purchase #3	$159.88	7.835%	$172.4066	$172.41	$172.40	$172.40
Purchase #4	$62.49	8.376%	$67.7242	$67.72	$67.70	$67.70
Purchase #5	$221.73	10.476%	$244.9584	$244.96	$244.95	$245.00
Purchase #6	$204.76	12.606%	$230.572	$230.57	$230.55	$230.60
Purchase #7	$78.54	3.479%	$81.2724	$81.27	$81.25	$81.30
7 purchase totals =	$995.63		$1,081.6098	$1,081.61	$1,081.50	$1,081.70