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	$9.48	5.591%	$10.01	$10.01	$10.00	$10.00
Purchase #2	$62.53	7.495%	$67.2166	$67.22	$67.20	$67.20
Purchase #3	$167.89	7.296%	$180.1393	$180.14	$180.15	$180.10
Purchase #4	$47.32	7.191%	$50.7228	$50.72	$50.70	$50.70
Purchase #5	$178.30	7.457%	$191.5958	$191.60	$191.60	$191.60
Purchase #6	$207.56	7.287%	$222.6849	$222.68	$222.70	$222.70
Purchase #7	$115.89	7.163%	$124.1912	$124.19	$124.20	$124.20
7 purchase totals =	$788.97		$846.5606	$846.56	$846.55	$846.50