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	$225.28	6.739%	$240.4616	$240.46	$240.45	$240.50
Purchase #2	$130.91	11.431%	$145.8743	$145.87	$145.85	$145.90
Purchase #3	$233.66	10.625%	$258.4864	$258.49	$258.50	$258.50
Purchase #4	$118.56	6.425%	$126.1775	$126.18	$126.20	$126.20
Purchase #5	$89.59	11.287%	$99.702	$99.70	$99.70	$99.70
Purchase #6	$148.49	12.395%	$166.8953	$166.90	$166.90	$166.90
Purchase #7	$233.61	4.258%	$243.5571	$243.56	$243.55	$243.60
7 purchase totals =	$1,180.10		$1,281.1542	$1,281.16	$1,281.15	$1,281.30