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	$29.49	10.587%	$32.6121	$32.61	$32.60	$32.60
Purchase #2	$159.87	8.850%	$174.0185	$174.02	$174.00	$174.00
Purchase #3	$7.33	5.863%	$7.7598	$7.76	$7.75	$7.80
Purchase #4	$54.53	13.857%	$62.0862	$62.09	$62.10	$62.10
Purchase #5	$230.60	7.339%	$247.5237	$247.52	$247.50	$247.50
Purchase #6	$100.48	3.470%	$103.9667	$103.97	$103.95	$104.00
Purchase #7	$195.76	10.612%	$216.5341	$216.53	$216.55	$216.50
7 purchase totals =	$778.06		$844.5011	$844.50	$844.45	$844.50