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	$34.84	10.771%	$38.5926	$38.59	$38.60	$38.60
Purchase #2	$6.88	11.764%	$7.6894	$7.69	$7.70	$7.70
Purchase #3	$86.46	3.633%	$89.6011	$89.60	$89.60	$89.60
Purchase #4	$219.65	11.339%	$244.5561	$244.56	$244.55	$244.60
Purchase #5	$34.30	8.327%	$37.1562	$37.16	$37.15	$37.20
Purchase #6	$51.47	7.236%	$55.1944	$55.19	$55.20	$55.20
Purchase #7	$228.67	12.411%	$257.0502	$257.05	$257.05	$257.10
7 purchase totals =	$662.27		$729.8400	$729.84	$729.85	$730.00