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	$156.68	9.216%	$171.1196	$171.12	$171.10	$171.10
Purchase #2	$162.25	10.655%	$179.5377	$179.54	$179.55	$179.50
Purchase #3	$133.92	8.619%	$145.4626	$145.46	$145.45	$145.50
Purchase #4	$38.68	13.535%	$43.9153	$43.92	$43.90	$43.90
Purchase #5	$173.31	11.860%	$193.8646	$193.86	$193.85	$193.90
Purchase #6	$101.71	12.559%	$114.4838	$114.48	$114.50	$114.50
Purchase #7	$141.85	3.235%	$146.4388	$146.44	$146.45	$146.40
7 purchase totals =	$908.40		$994.8224	$994.82	$994.80	$994.80