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	$17.93	12.852%	$20.2344	$20.23	$20.25	$20.20
Purchase #2	$93.34	7.721%	$100.5468	$100.55	$100.55	$100.50
Purchase #3	$18.56	10.750%	$20.5552	$20.56	$20.55	$20.60
Purchase #4	$227.39	6.641%	$242.491	$242.49	$242.50	$242.50
Purchase #5	$32.78	7.679%	$35.2972	$35.30	$35.30	$35.30
Purchase #6	$66.85	6.557%	$71.2334	$71.23	$71.25	$71.20
Purchase #7	$222.65	7.752%	$239.9098	$239.91	$239.90	$239.90
7 purchase totals =	$679.50		$730.2678	$730.27	$730.30	$730.20