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	$5.59	4.126%	$5.8206	$5.82	$5.80	$5.80
Purchase #2	$173.80	10.237%	$191.5919	$191.59	$191.60	$191.60
Purchase #3	$57.72	7.220%	$61.8874	$61.89	$61.90	$61.90
Purchase #4	$231.80	6.719%	$247.3746	$247.37	$247.35	$247.40
Purchase #5	$116.34	9.436%	$127.3178	$127.32	$127.30	$127.30
Purchase #6	$107.91	3.860%	$112.0753	$112.08	$112.10	$112.10
Purchase #7	$32.90	13.184%	$37.2375	$37.24	$37.25	$37.20
7 purchase totals =	$726.06		$783.3051	$783.31	$783.30	$783.30