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	$24.76	9.734%	$27.1701	$27.17	$27.15	$27.20
Purchase #2	$126.59	10.213%	$139.5186	$139.52	$139.50	$139.50
Purchase #3	$132.52	5.277%	$139.5131	$139.51	$139.50	$139.50
Purchase #4	$61.26	13.194%	$69.3426	$69.34	$69.35	$69.30
Purchase #5	$139.58	6.717%	$148.9556	$148.96	$148.95	$149.00
Purchase #6	$156.52	13.735%	$178.018	$178.02	$178.00	$178.00
Purchase #7	$124.90	13.302%	$141.5142	$141.51	$141.50	$141.50
7 purchase totals =	$766.13		$844.0322	$844.03	$843.95	$844.00