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	$69.73	5.152%	$73.3225	$73.32	$73.30	$73.30
Purchase #2	$222.87	13.204%	$252.2978	$252.30	$252.30	$252.30
Purchase #3	$95.25	11.822%	$106.5105	$106.51	$106.50	$106.50
Purchase #4	$18.65	3.392%	$19.2826	$19.28	$19.30	$19.30
Purchase #5	$104.37	7.352%	$112.0433	$112.04	$112.05	$112.00
Purchase #6	$111.93	10.363%	$123.5293	$123.53	$123.55	$123.50
Purchase #7	$89.87	13.622%	$102.1121	$102.11	$102.10	$102.10
7 purchase totals =	$712.67		$789.0981	$789.09	$789.10	$789.00