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	$7.50	6.390%	$7.9793	$7.98	$8.00	$8.00
Purchase #2	$53.39	4.635%	$55.8646	$55.86	$55.85	$55.90
Purchase #3	$91.73	5.146%	$96.4504	$96.45	$96.45	$96.50
Purchase #4	$243.60	4.384%	$254.2794	$254.28	$254.30	$254.30
Purchase #5	$236.30	3.257%	$243.9963	$244.00	$244.00	$244.00
Purchase #6	$17.45	5.539%	$18.4166	$18.42	$18.40	$18.40
Purchase #7	$93.72	10.460%	$103.5231	$103.52	$103.50	$103.50
7 purchase totals =	$743.69		$780.5097	$780.51	$780.50	$780.60