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	$204.79	8.655%	$222.5146	$222.51	$222.50	$222.50
Purchase #2	$151.99	8.868%	$165.4685	$165.47	$165.45	$165.50
Purchase #3	$91.72	8.497%	$99.5134	$99.51	$99.50	$99.50
Purchase #4	$94.83	11.128%	$105.3827	$105.38	$105.40	$105.40
Purchase #5	$126.46	3.566%	$130.9696	$130.97	$130.95	$131.00
Purchase #6	$37.83	12.632%	$42.6087	$42.61	$42.60	$42.60
Purchase #7	$44.30	3.195%	$45.7154	$45.72	$45.70	$45.70
7 purchase totals =	$751.92		$812.1729	$812.17	$812.10	$812.20