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	$228.55	11.589%	$255.0367	$255.04	$255.05	$255.00
Purchase #2	$26.37	5.842%	$27.9105	$27.91	$27.90	$27.90
Purchase #3	$66.46	12.141%	$74.5289	$74.53	$74.55	$74.50
Purchase #4	$100.42	4.679%	$105.1187	$105.12	$105.10	$105.10
Purchase #5	$32.67	3.393%	$33.7785	$33.78	$33.80	$33.80
Purchase #6	$106.58	4.679%	$111.5669	$111.57	$111.55	$111.60
Purchase #7	$68.83	3.195%	$71.0291	$71.03	$71.05	$71.00
7 purchase totals =	$629.88		$678.9693	$678.98	$679.00	$678.90