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	$126.68	7.840%	$136.6117	$136.61	$136.60	$136.60
Purchase #2	$242.38	9.238%	$264.7711	$264.77	$264.75	$264.80
Purchase #3	$47.54	6.864%	$50.8031	$50.80	$50.80	$50.80
Purchase #4	$55.89	6.434%	$59.486	$59.49	$59.50	$59.50
Purchase #5	$134.76	5.436%	$142.0856	$142.09	$142.10	$142.10
Purchase #6	$219.27	13.381%	$248.6105	$248.61	$248.60	$248.60
Purchase #7	$152.96	10.615%	$169.1967	$169.20	$169.20	$169.20
7 purchase totals =	$979.48		$1,071.5647	$1,071.57	$1,071.55	$1,071.60