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	$73.64	8.471%	$79.878	$79.88	$79.90	$79.90
Purchase #2	$106.64	11.154%	$118.5346	$118.53	$118.55	$118.50
Purchase #3	$146.41	9.569%	$160.42	$160.42	$160.40	$160.40
Purchase #4	$116.72	8.174%	$126.2607	$126.26	$126.25	$126.30
Purchase #5	$137.99	11.223%	$153.4766	$153.48	$153.50	$153.50
Purchase #6	$174.78	9.539%	$191.4523	$191.45	$191.45	$191.50
Purchase #7	$115.38	10.375%	$127.3507	$127.35	$127.35	$127.40
7 purchase totals =	$871.56		$957.3729	$957.37	$957.40	$957.50