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	$74.49	8.536%	$80.8485	$80.85	$80.85	$80.80
Purchase #2	$36.34	5.340%	$38.2806	$38.28	$38.30	$38.30
Purchase #3	$30.27	12.524%	$34.061	$34.06	$34.05	$34.10
Purchase #4	$49.82	13.102%	$56.3474	$56.35	$56.35	$56.30
Purchase #5	$128.82	12.487%	$144.9058	$144.91	$144.90	$144.90
Purchase #6	$165.41	8.758%	$179.8966	$179.90	$179.90	$179.90
Purchase #7	$84.46	5.431%	$89.047	$89.05	$89.05	$89.00
7 purchase totals =	$569.61		$623.3869	$623.40	$623.40	$623.30