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	$244.98	4.281%	$255.4676	$255.47	$255.45	$255.50
Purchase #2	$106.89	8.153%	$115.6047	$115.60	$115.60	$115.60
Purchase #3	$149.46	7.159%	$160.1598	$160.16	$160.15	$160.20
Purchase #4	$225.58	11.216%	$250.8811	$250.88	$250.90	$250.90
Purchase #5	$145.96	13.511%	$165.6807	$165.68	$165.70	$165.70
Purchase #6	$45.51	10.824%	$50.436	$50.44	$50.45	$50.40
Purchase #7	$144.80	8.825%	$157.5786	$157.58	$157.60	$157.60
7 purchase totals =	$1,063.18		$1,155.8085	$1,155.81	$1,155.85	$1,155.90