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	$150.38	5.807%	$159.1126	$159.11	$159.10	$159.10
Purchase #2	$151.82	3.329%	$156.8741	$156.87	$156.85	$156.90
Purchase #3	$117.92	8.274%	$127.6767	$127.68	$127.70	$127.70
Purchase #4	$181.56	10.316%	$200.2897	$200.29	$200.30	$200.30
Purchase #5	$118.65	10.833%	$131.5034	$131.50	$131.50	$131.50
Purchase #6	$25.35	11.403%	$28.2407	$28.24	$28.25	$28.20
Purchase #7	$99.85	7.288%	$107.1271	$107.13	$107.15	$107.10
7 purchase totals =	$845.53		$910.8243	$910.82	$910.85	$910.80