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	$16.61	10.778%	$18.4002	$18.40	$18.40	$18.40
Purchase #2	$101.60	12.133%	$113.9271	$113.93	$113.95	$113.90
Purchase #3	$170.96	10.297%	$188.5638	$188.56	$188.55	$188.60
Purchase #4	$54.70	3.405%	$56.5625	$56.56	$56.55	$56.60
Purchase #5	$65.94	7.267%	$70.7319	$70.73	$70.75	$70.70
Purchase #6	$180.78	5.807%	$191.2779	$191.28	$191.30	$191.30
Purchase #7	$245.91	13.802%	$279.8505	$279.85	$279.85	$279.90
7 purchase totals =	$836.50		$919.3139	$919.31	$919.35	$919.40