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	$119.85	13.551%	$136.0909	$136.09	$136.10	$136.10
Purchase #2	$111.32	10.690%	$123.2201	$123.22	$123.20	$123.20
Purchase #3	$238.27	7.110%	$255.211	$255.21	$255.20	$255.20
Purchase #4	$174.78	11.147%	$194.2627	$194.26	$194.25	$194.30
Purchase #5	$248.90	8.173%	$269.2426	$269.24	$269.25	$269.20
Purchase #6	$202.90	8.325%	$219.7914	$219.79	$219.80	$219.80
Purchase #7	$74.45	10.306%	$82.1228	$82.12	$82.10	$82.10
7 purchase totals =	$1,170.47		$1,279.9415	$1,279.93	$1,279.90	$1,279.90