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	$244.93	13.265%	$277.42	$277.42	$277.40	$277.40
Purchase #2	$53.37	11.555%	$59.5369	$59.54	$59.55	$59.50
Purchase #3	$44.43	5.375%	$46.8181	$46.82	$46.80	$46.80
Purchase #4	$175.81	10.616%	$194.474	$194.47	$194.45	$194.50
Purchase #5	$46.61	11.485%	$51.9632	$51.96	$51.95	$52.00
Purchase #6	$50.77	4.833%	$53.2237	$53.22	$53.20	$53.20
Purchase #7	$219.56	4.860%	$230.2306	$230.23	$230.25	$230.20
7 purchase totals =	$835.48		$913.6665	$913.66	$913.60	$913.60