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	$44.76	12.312%	$50.2709	$50.27	$50.25	$50.30
Purchase #2	$53.66	10.330%	$59.2031	$59.20	$59.20	$59.20
Purchase #3	$188.45	11.395%	$209.9239	$209.92	$209.90	$209.90
Purchase #4	$53.92	6.786%	$57.579	$57.58	$57.60	$57.60
Purchase #5	$230.65	13.593%	$262.0023	$262.00	$262.00	$262.00
Purchase #6	$115.98	6.798%	$123.8643	$123.86	$123.85	$123.90
Purchase #7	$86.45	3.130%	$89.1559	$89.16	$89.15	$89.20
7 purchase totals =	$773.87		$851.9994	$851.99	$851.95	$852.10