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	$142.47	10.174%	$156.9649	$156.96	$156.95	$157.00
Purchase #2	$60.81	9.848%	$66.7986	$66.80	$66.80	$66.80
Purchase #3	$111.94	10.420%	$123.6041	$123.60	$123.60	$123.60
Purchase #4	$234.75	5.124%	$246.7786	$246.78	$246.80	$246.80
Purchase #5	$45.30	11.423%	$50.4746	$50.47	$50.45	$50.50
Purchase #6	$26.72	6.718%	$28.515	$28.52	$28.50	$28.50
Purchase #7	$165.68	12.147%	$185.8051	$185.81	$185.80	$185.80
7 purchase totals =	$787.67		$858.9409	$858.94	$858.90	$859.00