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	$95.50	5.625%	$100.8719	$100.87	$100.85	$100.90
Purchase #2	$203.89	6.595%	$217.3365	$217.34	$217.35	$217.30
Purchase #3	$111.72	13.719%	$127.0469	$127.05	$127.05	$127.00
Purchase #4	$129.85	6.580%	$138.3941	$138.39	$138.40	$138.40
Purchase #5	$244.79	13.112%	$276.8869	$276.89	$276.90	$276.90
Purchase #6	$165.66	8.647%	$179.9846	$179.98	$180.00	$180.00
Purchase #7	$220.51	8.779%	$239.8686	$239.87	$239.85	$239.90
7 purchase totals =	$1,171.92		$1,280.3895	$1,280.39	$1,280.40	$1,280.40