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	$81.91	10.769%	$90.7309	$90.73	$90.75	$90.70
Purchase #2	$112.99	12.502%	$127.116	$127.12	$127.10	$127.10
Purchase #3	$172.45	10.689%	$190.8832	$190.88	$190.90	$190.90
Purchase #4	$80.38	10.419%	$88.7548	$88.75	$88.75	$88.80
Purchase #5	$12.75	11.165%	$14.1735	$14.17	$14.15	$14.20
Purchase #6	$137.32	10.549%	$151.8059	$151.81	$151.80	$151.80
Purchase #7	$188.99	11.123%	$210.0114	$210.01	$210.00	$210.00
7 purchase totals =	$786.79		$873.4757	$873.47	$873.45	$873.50