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	$90.44	10.667%	$100.0872	$100.09	$100.10	$100.10
Purchase #2	$246.48	3.329%	$254.6853	$254.69	$254.70	$254.70
Purchase #3	$10.98	13.769%	$12.4918	$12.49	$12.50	$12.50
Purchase #4	$126.92	11.798%	$141.894	$141.89	$141.90	$141.90
Purchase #5	$160.79	7.241%	$172.4328	$172.43	$172.45	$172.40
Purchase #6	$8.37	7.620%	$9.0078	$9.01	$9.00	$9.00
Purchase #7	$137.67	5.855%	$145.7306	$145.73	$145.75	$145.70
7 purchase totals =	$781.65		$836.3295	$836.33	$836.40	$836.30