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	$85.78	7.126%	$91.8927	$91.89	$91.90	$91.90
Purchase #2	$95.89	12.240%	$107.6269	$107.63	$107.65	$107.60
Purchase #3	$242.37	11.448%	$270.1165	$270.12	$270.10	$270.10
Purchase #4	$106.26	11.526%	$118.5075	$118.51	$118.50	$118.50
Purchase #5	$121.71	4.768%	$127.5131	$127.51	$127.50	$127.50
Purchase #6	$46.69	13.855%	$53.1589	$53.16	$53.15	$53.20
Purchase #7	$230.53	8.624%	$250.4109	$250.41	$250.40	$250.40
7 purchase totals =	$929.23		$1,019.2265	$1,019.23	$1,019.20	$1,019.20