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	$81.66	9.136%	$89.1205	$89.12	$89.10	$89.10
Purchase #2	$68.98	6.261%	$73.2988	$73.30	$73.30	$73.30
Purchase #3	$123.50	13.333%	$139.9663	$139.97	$139.95	$140.00
Purchase #4	$88.59	13.418%	$100.477	$100.48	$100.50	$100.50
Purchase #5	$220.43	8.748%	$239.7132	$239.71	$239.70	$239.70
Purchase #6	$45.69	11.852%	$51.1052	$51.11	$51.10	$51.10
Purchase #7	$151.55	5.199%	$159.4291	$159.43	$159.45	$159.40
7 purchase totals =	$780.40		$853.1101	$853.12	$853.10	$853.10