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	$112.56	3.474%	$116.4703	$116.47	$116.45	$116.50
Purchase #2	$206.28	6.177%	$219.0219	$219.02	$219.00	$219.00
Purchase #3	$244.34	4.371%	$255.0201	$255.02	$255.00	$255.00
Purchase #4	$210.93	5.773%	$223.107	$223.11	$223.10	$223.10
Purchase #5	$62.83	12.789%	$70.8653	$70.87	$70.85	$70.90
Purchase #6	$148.41	3.407%	$153.4663	$153.47	$153.45	$153.50
Purchase #7	$144.75	4.504%	$151.2695	$151.27	$151.25	$151.30
7 purchase totals =	$1,130.10		$1,189.2204	$1,189.23	$1,189.10	$1,189.30