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	$82.99	9.279%	$90.6906	$90.69	$90.70	$90.70
Purchase #2	$51.94	9.447%	$56.8468	$56.85	$56.85	$56.80
Purchase #3	$22.66	8.791%	$24.652	$24.65	$24.65	$24.70
Purchase #4	$35.30	11.160%	$39.2395	$39.24	$39.25	$39.20
Purchase #5	$65.33	12.666%	$73.6047	$73.60	$73.60	$73.60
Purchase #6	$147.45	8.125%	$159.4303	$159.43	$159.45	$159.40
Purchase #7	$29.50	10.222%	$32.5155	$32.52	$32.50	$32.50
7 purchase totals =	$435.17		$476.9794	$476.98	$477.00	$476.90