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	$33.32	7.667%	$35.8746	$35.87	$35.85	$35.90
Purchase #2	$120.67	5.113%	$126.8399	$126.84	$126.85	$126.80
Purchase #3	$82.46	9.286%	$90.1172	$90.12	$90.10	$90.10
Purchase #4	$131.66	11.487%	$146.7838	$146.78	$146.80	$146.80
Purchase #5	$170.33	13.471%	$193.2752	$193.28	$193.30	$193.30
Purchase #6	$104.59	7.584%	$112.5221	$112.52	$112.50	$112.50
Purchase #7	$63.53	4.679%	$66.5026	$66.50	$66.50	$66.50
7 purchase totals =	$706.56		$771.9154	$771.91	$771.90	$771.90