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	$17.55	4.281%	$18.3013	$18.30	$18.30	$18.30
Purchase #2	$92.72	13.249%	$105.0045	$105.00	$105.00	$105.00
Purchase #3	$18.47	9.326%	$20.1925	$20.19	$20.20	$20.20
Purchase #4	$112.37	3.524%	$116.3299	$116.33	$116.35	$116.30
Purchase #5	$100.25	5.346%	$105.6094	$105.61	$105.60	$105.60
Purchase #6	$101.90	10.117%	$112.2092	$112.21	$112.20	$112.20
Purchase #7	$169.39	12.124%	$189.9268	$189.93	$189.95	$189.90
7 purchase totals =	$612.65		$667.5736	$667.57	$667.60	$667.50