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	$27.80	12.139%	$31.1746	$31.17	$31.15	$31.20
Purchase #2	$140.49	5.187%	$147.7772	$147.78	$147.80	$147.80
Purchase #3	$146.25	5.525%	$154.3303	$154.33	$154.35	$154.30
Purchase #4	$198.92	11.855%	$222.502	$222.50	$222.50	$222.50
Purchase #5	$129.76	13.459%	$147.2244	$147.22	$147.20	$147.20
Purchase #6	$231.83	6.683%	$247.3232	$247.32	$247.30	$247.30
Purchase #7	$48.98	9.103%	$53.4386	$53.44	$53.45	$53.40
7 purchase totals =	$924.03		$1,003.7703	$1,003.76	$1,003.75	$1,003.70