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	$10.71	13.578%	$12.1642	$12.16	$12.15	$12.20
Purchase #2	$125.30	13.346%	$142.0225	$142.02	$142.00	$142.00
Purchase #3	$66.49	7.471%	$71.4575	$71.46	$71.45	$71.50
Purchase #4	$127.68	4.742%	$133.7346	$133.73	$133.75	$133.70
Purchase #5	$139.82	10.111%	$153.9572	$153.96	$153.95	$154.00
Purchase #6	$28.93	7.771%	$31.1782	$31.18	$31.20	$31.20
Purchase #7	$100.74	4.526%	$105.2995	$105.30	$105.30	$105.30
7 purchase totals =	$599.67		$649.8137	$649.81	$649.80	$649.90