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	$242.87	5.236%	$255.5867	$255.59	$255.60	$255.60
Purchase #2	$243.60	9.648%	$267.1025	$267.10	$267.10	$267.10
Purchase #3	$137.58	6.290%	$146.2338	$146.23	$146.25	$146.20
Purchase #4	$116.64	10.481%	$128.865	$128.87	$128.85	$128.90
Purchase #5	$35.47	12.353%	$39.8516	$39.85	$39.85	$39.90
Purchase #6	$62.49	4.816%	$65.4995	$65.50	$65.50	$65.50
Purchase #7	$73.63	5.673%	$77.807	$77.81	$77.80	$77.80
7 purchase totals =	$912.28		$980.9461	$980.95	$980.95	$981.00