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	$120.53	6.522%	$128.391	$128.39	$128.40	$128.40
Purchase #2	$32.29	10.112%	$35.5552	$35.56	$35.55	$35.60
Purchase #3	$65.47	10.593%	$72.4052	$72.41	$72.40	$72.40
Purchase #4	$42.95	4.864%	$45.0391	$45.04	$45.05	$45.00
Purchase #5	$90.78	10.681%	$100.4762	$100.48	$100.50	$100.50
Purchase #6	$115.74	9.841%	$127.13	$127.13	$127.15	$127.10
Purchase #7	$126.27	5.643%	$133.3954	$133.40	$133.40	$133.40
7 purchase totals =	$594.03		$642.3921	$642.41	$642.45	$642.40