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	$82.45	3.277%	$85.1519	$85.15	$85.15	$85.20
Purchase #2	$76.87	13.108%	$86.9461	$86.95	$86.95	$86.90
Purchase #3	$97.73	13.776%	$111.1933	$111.19	$111.20	$111.20
Purchase #4	$34.49	11.405%	$38.4236	$38.42	$38.40	$38.40
Purchase #5	$137.80	6.468%	$146.7129	$146.71	$146.70	$146.70
Purchase #6	$155.68	8.281%	$168.5719	$168.57	$168.55	$168.60
Purchase #7	$106.59	8.674%	$115.8356	$115.84	$115.85	$115.80
7 purchase totals =	$691.61		$752.8353	$752.83	$752.80	$752.80