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	$78.47	8.638%	$85.2482	$85.25	$85.25	$85.20
Purchase #2	$241.72	3.589%	$250.3953	$250.40	$250.40	$250.40
Purchase #3	$75.88	10.239%	$83.6494	$83.65	$83.65	$83.60
Purchase #4	$26.64	5.569%	$28.1236	$28.12	$28.10	$28.10
Purchase #5	$142.85	3.401%	$147.7083	$147.71	$147.70	$147.70
Purchase #6	$83.30	7.697%	$89.7116	$89.71	$89.70	$89.70
Purchase #7	$83.61	13.523%	$94.9166	$94.92	$94.90	$94.90
7 purchase totals =	$732.47		$779.7530	$779.76	$779.70	$779.60