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	$24.81	9.685%	$27.2128	$27.21	$27.20	$27.20
Purchase #2	$18.90	8.392%	$20.4861	$20.49	$20.50	$20.50
Purchase #3	$230.41	10.550%	$254.7183	$254.72	$254.70	$254.70
Purchase #4	$83.76	7.685%	$90.197	$90.20	$90.20	$90.20
Purchase #5	$137.64	5.551%	$145.2804	$145.28	$145.30	$145.30
Purchase #6	$94.35	5.500%	$99.5393	$99.54	$99.55	$99.50
Purchase #7	$81.73	10.638%	$90.4244	$90.42	$90.40	$90.40
7 purchase totals =	$671.60		$727.8583	$727.86	$727.85	$727.80