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	$229.64	4.734%	$240.5112	$240.51	$240.50	$240.50
Purchase #2	$120.57	11.665%	$134.6345	$134.63	$134.65	$134.60
Purchase #3	$241.81	5.244%	$254.4905	$254.49	$254.50	$254.50
Purchase #4	$180.56	5.852%	$191.1264	$191.13	$191.15	$191.10
Purchase #5	$119.76	6.460%	$127.4965	$127.50	$127.50	$127.50
Purchase #6	$27.59	6.688%	$29.4352	$29.44	$29.45	$29.40
Purchase #7	$48.86	8.610%	$53.0668	$53.07	$53.05	$53.10
7 purchase totals =	$968.79		$1,030.7611	$1,030.77	$1,030.80	$1,030.70