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	$70.76	6.137%	$75.1025	$75.10	$75.10	$75.10
Purchase #2	$167.57	4.346%	$174.8526	$174.85	$174.85	$174.90
Purchase #3	$223.42	10.501%	$246.8813	$246.88	$246.90	$246.90
Purchase #4	$206.58	13.164%	$233.7742	$233.77	$233.75	$233.80
Purchase #5	$116.55	6.298%	$123.8903	$123.89	$123.90	$123.90
Purchase #6	$246.30	3.775%	$255.5978	$255.60	$255.60	$255.60
Purchase #7	$117.97	8.800%	$128.3514	$128.35	$128.35	$128.40
7 purchase totals =	$1,149.15		$1,238.4501	$1,238.44	$1,238.45	$1,238.60