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	$37.90	13.500%	$43.0165	$43.02	$43.00	$43.00
Purchase #2	$206.86	7.817%	$223.0302	$223.03	$223.05	$223.00
Purchase #3	$226.54	4.742%	$237.2825	$237.28	$237.30	$237.30
Purchase #4	$170.76	8.753%	$185.7066	$185.71	$185.70	$185.70
Purchase #5	$137.69	8.788%	$149.7902	$149.79	$149.80	$149.80
Purchase #6	$51.92	3.689%	$53.8353	$53.84	$53.85	$53.80
Purchase #7	$70.33	10.748%	$77.8891	$77.89	$77.90	$77.90
7 purchase totals =	$902.00		$970.5504	$970.56	$970.60	$970.50