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	$90.92	10.223%	$100.2148	$100.21	$100.20	$100.20
Purchase #2	$98.27	13.453%	$111.4903	$111.49	$111.50	$111.50
Purchase #3	$181.30	7.683%	$195.2293	$195.23	$195.25	$195.20
Purchase #4	$73.82	8.463%	$80.0674	$80.07	$80.05	$80.10
Purchase #5	$247.38	3.187%	$255.264	$255.26	$255.25	$255.30
Purchase #6	$164.77	10.704%	$182.407	$182.41	$182.40	$182.40
Purchase #7	$18.46	4.667%	$19.3215	$19.32	$19.30	$19.30
7 purchase totals =	$874.92		$943.9943	$943.99	$943.95	$944.00