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	$250.57	3.136%	$258.4279	$258.43	$258.45	$258.40
Purchase #2	$189.29	3.701%	$196.2956	$196.30	$196.30	$196.30
Purchase #3	$154.89	3.103%	$159.6962	$159.70	$159.70	$159.70
Purchase #4	$154.88	12.542%	$174.305	$174.31	$174.30	$174.30
Purchase #5	$65.77	13.721%	$74.7943	$74.79	$74.80	$74.80
Purchase #6	$97.33	7.379%	$104.512	$104.51	$104.50	$104.50
Purchase #7	$68.40	4.143%	$71.2338	$71.23	$71.25	$71.20
7 purchase totals =	$981.13		$1,039.2648	$1,039.27	$1,039.30	$1,039.20