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	$27.39	3.395%	$28.3199	$28.32	$28.30	$28.30
Purchase #2	$183.77	12.375%	$206.5115	$206.51	$206.50	$206.50
Purchase #3	$150.51	5.243%	$158.4012	$158.40	$158.40	$158.40
Purchase #4	$69.81	10.521%	$77.1547	$77.15	$77.15	$77.20
Purchase #5	$142.25	6.754%	$151.8576	$151.86	$151.85	$151.90
Purchase #6	$56.60	6.698%	$60.3911	$60.39	$60.40	$60.40
Purchase #7	$241.40	9.454%	$264.222	$264.22	$264.20	$264.20
7 purchase totals =	$871.73		$946.8580	$946.85	$946.80	$946.90