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	$103.62	9.833%	$113.809	$113.81	$113.80	$113.80
Purchase #2	$128.41	13.172%	$145.3242	$145.32	$145.30	$145.30
Purchase #3	$210.90	9.130%	$230.1552	$230.16	$230.15	$230.20
Purchase #4	$90.95	9.488%	$99.5793	$99.58	$99.60	$99.60
Purchase #5	$54.59	12.420%	$61.3701	$61.37	$61.35	$61.40
Purchase #6	$54.78	4.173%	$57.066	$57.07	$57.05	$57.10
Purchase #7	$133.45	3.503%	$138.1248	$138.12	$138.10	$138.10
7 purchase totals =	$776.70		$845.4286	$845.43	$845.35	$845.50