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	$36.75	11.161%	$40.8517	$40.85	$40.85	$40.90
Purchase #2	$16.89	12.287%	$18.9653	$18.97	$18.95	$19.00
Purchase #3	$163.56	5.490%	$172.5394	$172.54	$172.55	$172.50
Purchase #4	$28.29	13.539%	$32.1202	$32.12	$32.10	$32.10
Purchase #5	$166.54	9.152%	$181.7817	$181.78	$181.80	$181.80
Purchase #6	$152.92	11.809%	$170.9783	$170.98	$171.00	$171.00
Purchase #7	$128.52	13.444%	$145.7982	$145.80	$145.80	$145.80
7 purchase totals =	$693.47		$763.0348	$763.04	$763.05	$763.10