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	$110.30	11.664%	$123.1654	$123.17	$123.15	$123.20
Purchase #2	$126.97	13.406%	$143.9916	$143.99	$144.00	$144.00
Purchase #3	$212.89	5.180%	$223.9177	$223.92	$223.90	$223.90
Purchase #4	$235.79	3.836%	$244.8349	$244.83	$244.85	$244.80
Purchase #5	$25.51	7.212%	$27.3498	$27.35	$27.35	$27.30
Purchase #6	$146.54	6.620%	$156.2409	$156.24	$156.25	$156.20
Purchase #7	$245.27	4.274%	$255.7528	$255.75	$255.75	$255.80
7 purchase totals =	$1,103.27		$1,175.2531	$1,175.25	$1,175.25	$1,175.20