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	$94.61	5.781%	$100.0794	$100.08	$100.10	$100.10
Purchase #2	$221.78	7.536%	$238.4933	$238.49	$238.50	$238.50
Purchase #3	$160.64	6.252%	$170.6832	$170.68	$170.70	$170.70
Purchase #4	$149.72	13.505%	$169.9397	$169.94	$169.95	$169.90
Purchase #5	$244.56	4.575%	$255.7486	$255.75	$255.75	$255.70
Purchase #6	$247.30	10.629%	$273.5855	$273.59	$273.60	$273.60
Purchase #7	$157.30	5.351%	$165.7171	$165.72	$165.70	$165.70
7 purchase totals =	$1,275.91		$1,374.2468	$1,374.25	$1,374.30	$1,374.20