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	$224.76	13.508%	$255.1206	$255.12	$255.10	$255.10
Purchase #2	$52.65	5.140%	$55.3562	$55.36	$55.35	$55.40
Purchase #3	$73.40	13.689%	$83.4477	$83.45	$83.45	$83.40
Purchase #4	$194.86	13.631%	$221.4214	$221.42	$221.40	$221.40
Purchase #5	$58.56	6.737%	$62.5052	$62.51	$62.50	$62.50
Purchase #6	$219.40	6.815%	$234.3521	$234.35	$234.35	$234.40
Purchase #7	$22.38	7.603%	$24.0816	$24.08	$24.10	$24.10
7 purchase totals =	$846.01		$936.2848	$936.29	$936.25	$936.30