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	$13.39	9.845%	$14.7082	$14.71	$14.70	$14.70
Purchase #2	$98.39	13.397%	$111.5713	$111.57	$111.55	$111.60
Purchase #3	$53.60	3.295%	$55.3661	$55.37	$55.35	$55.40
Purchase #4	$99.80	6.114%	$105.9018	$105.90	$105.90	$105.90
Purchase #5	$141.90	3.705%	$147.1574	$147.16	$147.15	$147.20
Purchase #6	$79.43	13.605%	$90.2365	$90.24	$90.25	$90.20
Purchase #7	$207.74	8.587%	$225.5786	$225.58	$225.60	$225.60
7 purchase totals =	$694.25		$750.5199	$750.53	$750.50	$750.60