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	$166.51	4.172%	$173.4568	$173.46	$173.45	$173.50
Purchase #2	$32.64	6.633%	$34.805	$34.81	$34.80	$34.80
Purchase #3	$185.81	9.476%	$203.4174	$203.42	$203.40	$203.40
Purchase #4	$6.98	13.254%	$7.9051	$7.91	$7.90	$7.90
Purchase #5	$123.75	6.504%	$131.7987	$131.80	$131.80	$131.80
Purchase #6	$157.57	13.803%	$179.3194	$179.32	$179.30	$179.30
Purchase #7	$131.50	12.251%	$147.6101	$147.61	$147.60	$147.60
7 purchase totals =	$804.76		$878.3125	$878.33	$878.25	$878.30