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	$155.93	6.765%	$166.4787	$166.48	$166.50	$166.50
Purchase #2	$16.59	9.259%	$18.1261	$18.13	$18.15	$18.10
Purchase #3	$134.65	9.800%	$147.8457	$147.85	$147.85	$147.80
Purchase #4	$92.82	3.408%	$95.9833	$95.98	$96.00	$96.00
Purchase #5	$34.31	4.278%	$35.7778	$35.78	$35.80	$35.80
Purchase #6	$229.71	8.466%	$249.1572	$249.16	$249.15	$249.20
Purchase #7	$31.87	11.312%	$35.4751	$35.48	$35.50	$35.50
7 purchase totals =	$695.88		$748.8439	$748.86	$748.95	$748.90