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	$73.47	9.281%	$80.2888	$80.29	$80.30	$80.30
Purchase #2	$201.54	9.235%	$220.1522	$220.15	$220.15	$220.20
Purchase #3	$75.92	7.271%	$81.4401	$81.44	$81.45	$81.40
Purchase #4	$153.88	10.131%	$169.4696	$169.47	$169.45	$169.50
Purchase #5	$146.34	3.467%	$151.4136	$151.41	$151.40	$151.40
Purchase #6	$127.33	13.563%	$144.5998	$144.60	$144.60	$144.60
Purchase #7	$161.83	6.498%	$172.3457	$172.35	$172.35	$172.30
7 purchase totals =	$940.31		$1,019.7098	$1,019.71	$1,019.70	$1,019.70