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	$91.58	10.149%	$100.8745	$100.87	$100.85	$100.90
Purchase #2	$144.25	7.389%	$154.9086	$154.91	$154.90	$154.90
Purchase #3	$123.41	8.634%	$134.0652	$134.07	$134.05	$134.10
Purchase #4	$196.64	7.508%	$211.4037	$211.40	$211.40	$211.40
Purchase #5	$122.62	13.776%	$139.5121	$139.51	$139.50	$139.50
Purchase #6	$113.59	10.498%	$125.5147	$125.51	$125.50	$125.50
Purchase #7	$32.92	8.143%	$35.6007	$35.60	$35.60	$35.60
7 purchase totals =	$825.01		$901.8795	$901.87	$901.80	$901.90