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	$20.96	11.185%	$23.3044	$23.30	$23.30	$23.30
Purchase #2	$250.31	3.310%	$258.5953	$258.60	$258.60	$258.60
Purchase #3	$52.75	12.480%	$59.3332	$59.33	$59.35	$59.30
Purchase #4	$48.77	3.528%	$50.4906	$50.49	$50.50	$50.50
Purchase #5	$45.50	10.238%	$50.1583	$50.16	$50.15	$50.20
Purchase #6	$117.33	10.690%	$129.8726	$129.87	$129.85	$129.90
Purchase #7	$205.55	3.481%	$212.7052	$212.71	$212.70	$212.70
7 purchase totals =	$741.17		$784.4596	$784.46	$784.45	$784.50