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	$17.46	4.559%	$18.256	$18.26	$18.25	$18.30
Purchase #2	$28.62	11.126%	$31.8043	$31.80	$31.80	$31.80
Purchase #3	$210.86	8.567%	$228.9244	$228.92	$228.90	$228.90
Purchase #4	$131.94	7.816%	$142.2524	$142.25	$142.25	$142.30
Purchase #5	$68.72	3.788%	$71.3231	$71.32	$71.30	$71.30
Purchase #6	$18.41	11.305%	$20.4913	$20.49	$20.50	$20.50
Purchase #7	$105.34	12.104%	$118.0904	$118.09	$118.10	$118.10
7 purchase totals =	$581.35		$631.1419	$631.13	$631.10	$631.20