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	$83.96	7.273%	$90.0664	$90.07	$90.05	$90.10
Purchase #2	$157.56	10.321%	$173.8218	$173.82	$173.80	$173.80
Purchase #3	$89.83	12.862%	$101.3839	$101.38	$101.40	$101.40
Purchase #4	$18.98	10.272%	$20.9296	$20.93	$20.95	$20.90
Purchase #5	$188.60	4.157%	$196.4401	$196.44	$196.45	$196.40
Purchase #6	$24.91	4.389%	$26.0033	$26.00	$26.00	$26.00
Purchase #7	$244.92	4.530%	$256.0149	$256.01	$256.00	$256.00
7 purchase totals =	$808.76		$864.6600	$864.65	$864.65	$864.60