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	$35.61	4.784%	$37.3136	$37.31	$37.30	$37.30
Purchase #2	$37.49	7.571%	$40.3284	$40.33	$40.35	$40.30
Purchase #3	$52.28	12.113%	$58.6127	$58.61	$58.60	$58.60
Purchase #4	$21.52	5.541%	$22.7124	$22.71	$22.70	$22.70
Purchase #5	$203.75	10.122%	$224.3736	$224.37	$224.35	$224.40
Purchase #6	$49.86	12.575%	$56.1299	$56.13	$56.15	$56.10
Purchase #7	$47.85	13.619%	$54.3667	$54.37	$54.35	$54.40
7 purchase totals =	$448.36		$493.8373	$493.83	$493.80	$493.80