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	$177.75	6.675%	$189.6148	$189.61	$189.60	$189.60
Purchase #2	$214.55	12.270%	$240.8753	$240.88	$240.90	$240.90
Purchase #3	$29.70	13.349%	$33.6647	$33.66	$33.65	$33.70
Purchase #4	$118.52	7.419%	$127.313	$127.31	$127.30	$127.30
Purchase #5	$101.73	5.509%	$107.3343	$107.33	$107.35	$107.30
Purchase #6	$137.28	9.300%	$150.047	$150.05	$150.05	$150.00
Purchase #7	$84.72	5.306%	$89.2152	$89.22	$89.20	$89.20
7 purchase totals =	$864.25		$938.0643	$938.06	$938.05	$938.00