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	$74.92	8.667%	$81.4133	$81.41	$81.40	$81.40
Purchase #2	$88.86	13.379%	$100.7486	$100.75	$100.75	$100.70
Purchase #3	$242.61	3.656%	$251.4798	$251.48	$251.50	$251.50
Purchase #4	$56.59	4.824%	$59.3199	$59.32	$59.30	$59.30
Purchase #5	$211.65	13.313%	$239.827	$239.83	$239.85	$239.80
Purchase #6	$108.99	3.223%	$112.5027	$112.50	$112.50	$112.50
Purchase #7	$26.82	10.243%	$29.5672	$29.57	$29.55	$29.60
7 purchase totals =	$810.44		$874.8585	$874.86	$874.85	$874.80