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	$51.72	5.371%	$54.4979	$54.50	$54.50	$54.50
Purchase #2	$202.25	11.803%	$226.1216	$226.12	$226.10	$226.10
Purchase #3	$42.99	13.852%	$48.945	$48.95	$48.95	$48.90
Purchase #4	$198.27	10.358%	$218.8068	$218.81	$218.80	$218.80
Purchase #5	$179.46	5.678%	$189.6497	$189.65	$189.65	$189.60
Purchase #6	$75.69	3.681%	$78.4761	$78.48	$78.50	$78.50
Purchase #7	$225.69	13.162%	$255.3953	$255.40	$255.40	$255.40
7 purchase totals =	$976.07		$1,071.8924	$1,071.91	$1,071.90	$1,071.80