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	$123.37	10.550%	$136.3855	$136.39	$136.40	$136.40
Purchase #2	$11.26	4.445%	$11.7605	$11.76	$11.75	$11.80
Purchase #3	$84.51	5.466%	$89.1293	$89.13	$89.15	$89.10
Purchase #4	$115.25	13.654%	$130.9862	$130.99	$131.00	$131.00
Purchase #5	$154.77	9.804%	$169.9437	$169.94	$169.95	$169.90
Purchase #6	$122.70	3.743%	$127.2927	$127.29	$127.30	$127.30
Purchase #7	$118.57	6.778%	$126.6067	$126.61	$126.60	$126.60
7 purchase totals =	$730.43		$792.1046	$792.11	$792.15	$792.10