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	$95.42	7.297%	$102.3828	$102.38	$102.40	$102.40
Purchase #2	$93.75	6.304%	$99.66	$99.66	$99.65	$99.70
Purchase #3	$114.54	13.578%	$130.0922	$130.09	$130.10	$130.10
Purchase #4	$94.54	6.570%	$100.7513	$100.75	$100.75	$100.80
Purchase #5	$132.70	12.254%	$148.9611	$148.96	$148.95	$149.00
Purchase #6	$22.69	10.777%	$25.1353	$25.14	$25.15	$25.10
Purchase #7	$54.93	12.682%	$61.8962	$61.90	$61.90	$61.90
7 purchase totals =	$608.57		$668.8789	$668.88	$668.90	$669.00