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	$79.52	12.426%	$89.4012	$89.40	$89.40	$89.40
Purchase #2	$192.42	12.746%	$216.9459	$216.95	$216.95	$216.90
Purchase #3	$54.65	10.710%	$60.503	$60.50	$60.50	$60.50
Purchase #4	$81.33	4.302%	$84.8288	$84.83	$84.85	$84.80
Purchase #5	$86.67	10.570%	$95.831	$95.83	$95.85	$95.80
Purchase #6	$105.51	12.589%	$118.7927	$118.79	$118.80	$118.80
Purchase #7	$12.85	12.760%	$14.4897	$14.49	$14.50	$14.50
7 purchase totals =	$612.95		$680.7923	$680.79	$680.85	$680.70