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	$64.28	7.492%	$69.0959	$69.10	$69.10	$69.10
Purchase #2	$86.32	3.137%	$89.0279	$89.03	$89.05	$89.00
Purchase #3	$38.90	6.681%	$41.4989	$41.50	$41.50	$41.50
Purchase #4	$212.46	9.791%	$233.262	$233.26	$233.25	$233.30
Purchase #5	$21.30	13.167%	$24.1046	$24.10	$24.10	$24.10
Purchase #6	$10.44	12.637%	$11.7593	$11.76	$11.75	$11.80
Purchase #7	$34.65	10.127%	$38.159	$38.16	$38.15	$38.20
7 purchase totals =	$468.35		$506.9076	$506.91	$506.90	$507.00