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	$37.68	6.854%	$40.2626	$40.26	$40.25	$40.30
Purchase #2	$129.50	11.718%	$144.6748	$144.67	$144.65	$144.70
Purchase #3	$238.42	7.498%	$256.2967	$256.30	$256.30	$256.30
Purchase #4	$158.36	8.247%	$171.4199	$171.42	$171.40	$171.40
Purchase #5	$126.89	3.139%	$130.8731	$130.87	$130.85	$130.90
Purchase #6	$248.88	10.157%	$274.1587	$274.16	$274.15	$274.20
Purchase #7	$37.87	9.625%	$41.515	$41.52	$41.50	$41.50
7 purchase totals =	$977.60		$1,059.2008	$1,059.20	$1,059.10	$1,059.30