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	$47.87	9.215%	$52.2812	$52.28	$52.30	$52.30
Purchase #2	$63.44	13.114%	$71.7595	$71.76	$71.75	$71.80
Purchase #3	$35.82	11.869%	$40.0715	$40.07	$40.05	$40.10
Purchase #4	$15.94	3.652%	$16.5221	$16.52	$16.50	$16.50
Purchase #5	$138.30	9.829%	$151.8935	$151.89	$151.90	$151.90
Purchase #6	$55.27	4.329%	$57.6626	$57.66	$57.65	$57.70
Purchase #7	$160.38	12.693%	$180.737	$180.74	$180.75	$180.70
7 purchase totals =	$517.02		$570.9274	$570.92	$570.90	$571.00