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	$35.90	6.266%	$38.1495	$38.15	$38.15	$38.10
Purchase #2	$151.93	8.379%	$164.6602	$164.66	$164.65	$164.70
Purchase #3	$31.81	4.231%	$33.1559	$33.16	$33.15	$33.20
Purchase #4	$28.90	13.196%	$32.7136	$32.71	$32.70	$32.70
Purchase #5	$65.52	3.269%	$67.6618	$67.66	$67.65	$67.70
Purchase #6	$87.79	8.559%	$95.3039	$95.30	$95.30	$95.30
Purchase #7	$122.45	6.114%	$129.9366	$129.94	$129.95	$129.90
7 purchase totals =	$524.30		$561.5815	$561.58	$561.55	$561.60