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	$111.97	5.635%	$118.2795	$118.28	$118.30	$118.30
Purchase #2	$104.66	11.811%	$117.0214	$117.02	$117.00	$117.00
Purchase #3	$38.34	7.336%	$41.1526	$41.15	$41.15	$41.20
Purchase #4	$66.98	5.319%	$70.5427	$70.54	$70.55	$70.50
Purchase #5	$80.83	9.335%	$88.3755	$88.38	$88.40	$88.40
Purchase #6	$104.69	9.306%	$114.4325	$114.43	$114.45	$114.40
Purchase #7	$228.45	11.647%	$255.0576	$255.06	$255.05	$255.10
7 purchase totals =	$735.92		$804.8618	$804.86	$804.90	$804.90