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	$237.77	8.739%	$258.5487	$258.55	$258.55	$258.50
Purchase #2	$60.71	6.772%	$64.8213	$64.82	$64.80	$64.80
Purchase #3	$19.52	8.205%	$21.1216	$21.12	$21.10	$21.10
Purchase #4	$134.34	11.822%	$150.2217	$150.22	$150.20	$150.20
Purchase #5	$205.64	7.700%	$221.4743	$221.47	$221.45	$221.50
Purchase #6	$132.41	5.363%	$139.5111	$139.51	$139.50	$139.50
Purchase #7	$191.76	4.549%	$200.4832	$200.48	$200.50	$200.50
7 purchase totals =	$982.15		$1,056.1819	$1,056.17	$1,056.10	$1,056.10