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	$9.92	11.392%	$11.0501	$11.05	$11.05	$11.10
Purchase #2	$55.80	6.121%	$59.2155	$59.22	$59.20	$59.20
Purchase #3	$18.82	10.677%	$20.8294	$20.83	$20.85	$20.80
Purchase #4	$112.68	12.296%	$126.5351	$126.54	$126.55	$126.50
Purchase #5	$126.30	10.796%	$139.9353	$139.94	$139.95	$139.90
Purchase #6	$107.60	7.352%	$115.5108	$115.51	$115.50	$115.50
Purchase #7	$36.45	9.834%	$40.0345	$40.03	$40.05	$40.00
7 purchase totals =	$467.57		$513.1107	$513.12	$513.15	$513.00