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	$13.88	7.131%	$14.8698	$14.87	$14.85	$14.90
Purchase #2	$33.30	12.747%	$37.5448	$37.54	$37.55	$37.50
Purchase #3	$129.62	3.616%	$134.3071	$134.31	$134.30	$134.30
Purchase #4	$98.55	13.351%	$111.7074	$111.71	$111.70	$111.70
Purchase #5	$30.74	3.449%	$31.8002	$31.80	$31.80	$31.80
Purchase #6	$48.62	3.128%	$50.1408	$50.14	$50.15	$50.10
Purchase #7	$199.93	6.154%	$212.2337	$212.23	$212.25	$212.20
7 purchase totals =	$554.64		$592.6038	$592.60	$592.60	$592.50