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	$100.25	10.849%	$111.1261	$111.13	$111.15	$111.10
Purchase #2	$137.87	3.389%	$142.5424	$142.54	$142.55	$142.50
Purchase #3	$157.94	4.791%	$165.5069	$165.51	$165.50	$165.50
Purchase #4	$223.53	6.847%	$238.8351	$238.84	$238.85	$238.80
Purchase #5	$182.73	3.594%	$189.2973	$189.30	$189.30	$189.30
Purchase #6	$67.50	4.709%	$70.6786	$70.68	$70.70	$70.70
Purchase #7	$77.54	13.164%	$87.7474	$87.75	$87.75	$87.70
7 purchase totals =	$947.36		$1,005.7338	$1,005.75	$1,005.80	$1,005.60