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	$217.74	10.141%	$239.821	$239.82	$239.80	$239.80
Purchase #2	$101.98	9.350%	$111.5151	$111.52	$111.50	$111.50
Purchase #3	$165.92	11.712%	$185.3526	$185.35	$185.35	$185.40
Purchase #4	$202.52	12.707%	$228.2542	$228.25	$228.25	$228.30
Purchase #5	$10.38	9.709%	$11.3878	$11.39	$11.40	$11.40
Purchase #6	$190.30	13.448%	$215.8915	$215.89	$215.90	$215.90
Purchase #7	$105.56	13.791%	$120.1178	$120.12	$120.10	$120.10
7 purchase totals =	$994.40		$1,112.3400	$1,112.34	$1,112.30	$1,112.40