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	$46.47	12.607%	$52.3285	$52.33	$52.35	$52.30
Purchase #2	$75.71	5.810%	$80.1088	$80.11	$80.10	$80.10
Purchase #3	$20.93	3.296%	$21.6199	$21.62	$21.60	$21.60
Purchase #4	$96.71	7.300%	$103.7698	$103.77	$103.75	$103.80
Purchase #5	$211.33	12.546%	$237.8435	$237.84	$237.85	$237.80
Purchase #6	$70.38	3.446%	$72.8053	$72.81	$72.80	$72.80
Purchase #7	$98.99	6.771%	$105.6926	$105.69	$105.70	$105.70
7 purchase totals =	$620.52		$674.1684	$674.17	$674.15	$674.10