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	$77.31	3.851%	$80.2872	$80.29	$80.30	$80.30
Purchase #2	$97.25	12.634%	$109.5366	$109.54	$109.55	$109.50
Purchase #3	$11.46	5.867%	$12.1324	$12.13	$12.15	$12.10
Purchase #4	$18.79	7.151%	$20.1337	$20.13	$20.15	$20.10
Purchase #5	$73.62	5.321%	$77.5373	$77.54	$77.55	$77.50
Purchase #6	$54.33	13.667%	$61.7553	$61.76	$61.75	$61.80
Purchase #7	$118.25	8.143%	$127.8791	$127.88	$127.90	$127.90
7 purchase totals =	$451.01		$489.2616	$489.27	$489.35	$489.20