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	$35.42	8.672%	$38.4916	$38.49	$38.50	$38.50
Purchase #2	$125.88	5.133%	$132.3414	$132.34	$132.35	$132.30
Purchase #3	$91.84	6.867%	$98.1467	$98.15	$98.15	$98.10
Purchase #4	$40.32	13.799%	$45.8838	$45.88	$45.90	$45.90
Purchase #5	$249.47	11.747%	$278.7752	$278.78	$278.80	$278.80
Purchase #6	$151.52	11.187%	$168.4705	$168.47	$168.45	$168.50
Purchase #7	$16.66	6.298%	$17.7092	$17.71	$17.70	$17.70
7 purchase totals =	$711.11		$779.8184	$779.82	$779.85	$779.80