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	$50.45	6.810%	$53.8856	$53.89	$53.90	$53.90
Purchase #2	$136.75	6.400%	$145.502	$145.50	$145.50	$145.50
Purchase #3	$57.38	7.121%	$61.466	$61.47	$61.45	$61.50
Purchase #4	$58.95	7.350%	$63.2828	$63.28	$63.30	$63.30
Purchase #5	$240.60	6.366%	$255.9166	$255.92	$255.90	$255.90
Purchase #6	$98.76	13.737%	$112.3267	$112.33	$112.35	$112.30
Purchase #7	$111.66	11.813%	$124.8504	$124.85	$124.85	$124.90
7 purchase totals =	$754.55		$817.2301	$817.24	$817.25	$817.30