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	$126.73	13.739%	$144.1414	$144.14	$144.15	$144.10
Purchase #2	$26.92	7.616%	$28.9702	$28.97	$28.95	$29.00
Purchase #3	$109.26	6.586%	$116.4559	$116.46	$116.45	$116.50
Purchase #4	$156.41	10.520%	$172.8643	$172.86	$172.85	$172.90
Purchase #5	$66.86	3.561%	$69.2409	$69.24	$69.25	$69.20
Purchase #6	$114.30	11.537%	$127.4868	$127.49	$127.50	$127.50
Purchase #7	$181.47	6.147%	$192.625	$192.63	$192.65	$192.60
7 purchase totals =	$781.95		$851.7845	$851.79	$851.80	$851.80