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	$34.90	7.367%	$37.4711	$37.47	$37.45	$37.50
Purchase #2	$42.37	10.285%	$46.7278	$46.73	$46.75	$46.70
Purchase #3	$117.49	6.734%	$125.4018	$125.40	$125.40	$125.40
Purchase #4	$47.48	5.654%	$50.1645	$50.16	$50.15	$50.20
Purchase #5	$231.43	10.245%	$255.14	$255.14	$255.15	$255.10
Purchase #6	$230.29	11.132%	$255.9259	$255.93	$255.95	$255.90
Purchase #7	$54.71	4.443%	$57.1408	$57.14	$57.15	$57.10
7 purchase totals =	$758.67		$827.9719	$827.97	$828.00	$827.90