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	$51.62	10.261%	$56.9167	$56.92	$56.90	$56.90
Purchase #2	$121.59	7.358%	$130.5366	$130.54	$130.55	$130.50
Purchase #3	$223.35	3.235%	$230.5754	$230.58	$230.60	$230.60
Purchase #4	$160.48	11.783%	$179.3894	$179.39	$179.40	$179.40
Purchase #5	$164.59	11.758%	$183.9425	$183.94	$183.95	$183.90
Purchase #6	$91.73	8.180%	$99.2335	$99.23	$99.25	$99.20
Purchase #7	$163.71	7.214%	$175.52	$175.52	$175.50	$175.50
7 purchase totals =	$977.07		$1,056.1141	$1,056.12	$1,056.15	$1,056.00