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	$39.40	8.228%	$42.6418	$42.64	$42.65	$42.60
Purchase #2	$115.98	6.320%	$123.3099	$123.31	$123.30	$123.30
Purchase #3	$165.56	4.672%	$173.295	$173.30	$173.30	$173.30
Purchase #4	$59.84	10.752%	$66.274	$66.27	$66.25	$66.30
Purchase #5	$209.97	8.555%	$227.9329	$227.93	$227.95	$227.90
Purchase #6	$31.34	5.567%	$33.0847	$33.08	$33.10	$33.10
Purchase #7	$144.88	11.549%	$161.6122	$161.61	$161.60	$161.60
7 purchase totals =	$766.97		$828.1505	$828.14	$828.15	$828.10