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	$35.49	8.275%	$38.4268	$38.43	$38.45	$38.40
Purchase #2	$235.50	11.200%	$261.876	$261.88	$261.90	$261.90
Purchase #3	$120.87	11.152%	$134.3494	$134.35	$134.35	$134.30
Purchase #4	$130.82	12.287%	$146.8939	$146.89	$146.90	$146.90
Purchase #5	$81.93	9.512%	$89.7232	$89.72	$89.70	$89.70
Purchase #6	$16.45	4.841%	$17.2463	$17.25	$17.25	$17.20
Purchase #7	$175.32	7.548%	$188.5532	$188.55	$188.55	$188.60
7 purchase totals =	$796.38		$877.0688	$877.07	$877.10	$877.00