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	$37.78	4.823%	$39.6021	$39.60	$39.60	$39.60
Purchase #2	$157.58	10.134%	$173.5492	$173.55	$173.55	$173.50
Purchase #3	$87.62	4.809%	$91.8336	$91.83	$91.85	$91.80
Purchase #4	$103.28	12.180%	$115.8595	$115.86	$115.85	$115.90
Purchase #5	$101.36	4.274%	$105.6921	$105.69	$105.70	$105.70
Purchase #6	$104.96	4.766%	$109.9624	$109.96	$109.95	$110.00
Purchase #7	$128.56	3.306%	$132.8102	$132.81	$132.80	$132.80
7 purchase totals =	$721.14		$769.3091	$769.30	$769.30	$769.30