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	$229.83	13.370%	$260.5583	$260.56	$260.55	$260.60
Purchase #2	$183.28	9.595%	$200.8657	$200.87	$200.85	$200.90
Purchase #3	$92.37	8.610%	$100.3231	$100.32	$100.30	$100.30
Purchase #4	$231.40	3.186%	$238.7724	$238.77	$238.75	$238.80
Purchase #5	$137.33	5.821%	$145.324	$145.32	$145.30	$145.30
Purchase #6	$195.86	9.654%	$214.7683	$214.77	$214.75	$214.80
Purchase #7	$92.50	6.363%	$98.3858	$98.39	$98.40	$98.40
7 purchase totals =	$1,162.57		$1,258.9976	$1,259.00	$1,258.90	$1,259.10