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	$243.85	4.501%	$254.8257	$254.83	$254.85	$254.80
Purchase #2	$104.47	13.451%	$118.5223	$118.52	$118.50	$118.50
Purchase #3	$68.93	13.647%	$78.3369	$78.34	$78.35	$78.30
Purchase #4	$204.79	8.573%	$222.3466	$222.35	$222.35	$222.30
Purchase #5	$138.55	5.728%	$146.4861	$146.49	$146.50	$146.50
Purchase #6	$240.72	9.851%	$264.4333	$264.43	$264.45	$264.40
Purchase #7	$55.75	13.612%	$63.3387	$63.34	$63.35	$63.30
7 purchase totals =	$1,057.06		$1,148.2896	$1,148.30	$1,148.35	$1,148.10