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	$234.63	12.562%	$264.1042	$264.10	$264.10	$264.10
Purchase #2	$166.79	3.152%	$172.0472	$172.05	$172.05	$172.00
Purchase #3	$48.55	9.233%	$53.0326	$53.03	$53.05	$53.00
Purchase #4	$30.95	11.302%	$34.448	$34.45	$34.45	$34.40
Purchase #5	$160.40	5.734%	$169.5973	$169.60	$169.60	$169.60
Purchase #6	$245.75	4.121%	$255.8774	$255.88	$255.90	$255.90
Purchase #7	$227.37	10.114%	$250.3662	$250.37	$250.35	$250.40
7 purchase totals =	$1,114.44		$1,199.4729	$1,199.48	$1,199.50	$1,199.40