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	$98.88	12.550%	$111.2894	$111.29	$111.30	$111.30
Purchase #2	$223.29	7.611%	$240.2846	$240.28	$240.30	$240.30
Purchase #3	$57.52	7.559%	$61.8679	$61.87	$61.85	$61.90
Purchase #4	$56.89	5.862%	$60.2249	$60.22	$60.20	$60.20
Purchase #5	$156.65	8.207%	$169.5063	$169.51	$169.50	$169.50
Purchase #6	$130.76	7.387%	$140.4192	$140.42	$140.40	$140.40
Purchase #7	$53.72	12.191%	$60.269	$60.27	$60.25	$60.30
7 purchase totals =	$777.71		$843.8613	$843.86	$843.80	$843.90