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	$140.93	9.457%	$154.2578	$154.26	$154.25	$154.30
Purchase #2	$110.37	6.139%	$117.1456	$117.15	$117.15	$117.10
Purchase #3	$171.82	3.201%	$177.32	$177.32	$177.30	$177.30
Purchase #4	$16.92	11.400%	$18.8489	$18.85	$18.85	$18.80
Purchase #5	$118.90	7.164%	$127.418	$127.42	$127.40	$127.40
Purchase #6	$118.58	10.592%	$131.14	$131.14	$131.15	$131.10
Purchase #7	$154.58	8.740%	$168.0903	$168.09	$168.10	$168.10
7 purchase totals =	$832.10		$894.2206	$894.23	$894.20	$894.10