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	$36.93	8.565%	$40.0931	$40.09	$40.10	$40.10
Purchase #2	$47.35	7.143%	$50.7322	$50.73	$50.75	$50.70
Purchase #3	$135.81	4.759%	$142.2732	$142.27	$142.25	$142.30
Purchase #4	$12.43	6.440%	$13.2305	$13.23	$13.25	$13.20
Purchase #5	$57.66	7.333%	$61.8882	$61.89	$61.90	$61.90
Purchase #6	$15.60	4.433%	$16.2915	$16.29	$16.30	$16.30
Purchase #7	$108.45	13.739%	$123.3499	$123.35	$123.35	$123.30
7 purchase totals =	$414.23		$447.8586	$447.85	$447.90	$447.80