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	$79.75	7.241%	$85.5247	$85.52	$85.50	$85.50
Purchase #2	$167.49	6.523%	$178.4154	$178.42	$178.40	$178.40
Purchase #3	$103.50	8.453%	$112.2489	$112.25	$112.25	$112.20
Purchase #4	$153.81	5.540%	$162.3311	$162.33	$162.35	$162.30
Purchase #5	$98.45	13.251%	$111.4956	$111.50	$111.50	$111.50
Purchase #6	$71.38	4.315%	$74.46	$74.46	$74.45	$74.50
Purchase #7	$113.51	7.402%	$121.912	$121.91	$121.90	$121.90
7 purchase totals =	$787.89		$846.3877	$846.39	$846.35	$846.30