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	$34.89	8.845%	$37.976	$37.98	$38.00	$38.00
Purchase #2	$242.50	11.819%	$271.1611	$271.16	$271.15	$271.20
Purchase #3	$112.59	11.465%	$125.4984	$125.50	$125.50	$125.50
Purchase #4	$97.64	5.586%	$103.0942	$103.09	$103.10	$103.10
Purchase #5	$142.58	8.408%	$154.5681	$154.57	$154.55	$154.60
Purchase #6	$240.85	5.146%	$253.2441	$253.24	$253.25	$253.20
Purchase #7	$132.33	6.190%	$140.5212	$140.52	$140.50	$140.50
7 purchase totals =	$1,003.38		$1,086.0631	$1,086.06	$1,086.05	$1,086.10