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	$69.28	3.233%	$71.5198	$71.52	$71.50	$71.50
Purchase #2	$149.63	7.361%	$160.6443	$160.64	$160.65	$160.60
Purchase #3	$81.39	10.702%	$90.1004	$90.10	$90.10	$90.10
Purchase #4	$167.52	6.686%	$178.7204	$178.72	$178.70	$178.70
Purchase #5	$162.84	10.339%	$179.676	$179.68	$179.70	$179.70
Purchase #6	$233.34	12.739%	$263.0652	$263.07	$263.05	$263.10
Purchase #7	$233.75	9.472%	$255.8908	$255.89	$255.90	$255.90
7 purchase totals =	$1,097.75		$1,199.6169	$1,199.62	$1,199.60	$1,199.60