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	$10.66	11.727%	$11.9101	$11.91	$11.90	$11.90
Purchase #2	$184.30	11.867%	$206.1709	$206.17	$206.15	$206.20
Purchase #3	$137.55	3.848%	$142.8429	$142.84	$142.85	$142.80
Purchase #4	$218.90	5.385%	$230.6878	$230.69	$230.70	$230.70
Purchase #5	$27.68	3.754%	$28.7191	$28.72	$28.70	$28.70
Purchase #6	$201.82	10.452%	$222.9142	$222.91	$222.90	$222.90
Purchase #7	$236.96	7.833%	$255.5211	$255.52	$255.50	$255.50
7 purchase totals =	$1,017.87		$1,098.7661	$1,098.76	$1,098.70	$1,098.70