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	$162.78	9.356%	$178.0097	$178.01	$178.00	$178.00
Purchase #2	$223.45	12.698%	$251.8237	$251.82	$251.80	$251.80
Purchase #3	$179.49	5.189%	$188.8037	$188.80	$188.80	$188.80
Purchase #4	$127.52	9.248%	$139.313	$139.31	$139.30	$139.30
Purchase #5	$224.51	11.603%	$250.5599	$250.56	$250.55	$250.60
Purchase #6	$144.27	9.395%	$157.8242	$157.82	$157.80	$157.80
Purchase #7	$86.51	4.205%	$90.1477	$90.15	$90.15	$90.10
7 purchase totals =	$1,148.53		$1,256.4819	$1,256.47	$1,256.40	$1,256.40