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	$66.27	10.314%	$73.1051	$73.11	$73.10	$73.10
Purchase #2	$155.77	3.740%	$161.5958	$161.60	$161.60	$161.60
Purchase #3	$90.68	12.624%	$102.1274	$102.13	$102.15	$102.10
Purchase #4	$53.36	3.690%	$55.329	$55.33	$55.35	$55.30
Purchase #5	$69.86	13.753%	$79.4678	$79.47	$79.45	$79.50
Purchase #6	$20.46	3.823%	$21.2422	$21.24	$21.25	$21.20
Purchase #7	$184.64	6.566%	$196.7635	$196.76	$196.75	$196.80
7 purchase totals =	$641.04		$689.6308	$689.64	$689.65	$689.60