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	$37.30	5.689%	$39.422	$39.42	$39.40	$39.40
Purchase #2	$144.60	11.496%	$161.2232	$161.22	$161.20	$161.20
Purchase #3	$147.71	9.678%	$162.0054	$162.01	$162.00	$162.00
Purchase #4	$88.81	6.478%	$94.5631	$94.56	$94.55	$94.60
Purchase #5	$179.56	10.762%	$198.8842	$198.88	$198.90	$198.90
Purchase #6	$105.66	4.820%	$110.7528	$110.75	$110.75	$110.80
Purchase #7	$211.75	13.628%	$240.6073	$240.61	$240.60	$240.60
7 purchase totals =	$915.39		$1,007.4580	$1,007.45	$1,007.40	$1,007.50