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	$168.66	8.720%	$183.3672	$183.37	$183.35	$183.40
Purchase #2	$241.71	11.722%	$270.0432	$270.04	$270.05	$270.00
Purchase #3	$29.50	9.796%	$32.3898	$32.39	$32.40	$32.40
Purchase #4	$56.44	9.536%	$61.8221	$61.82	$61.80	$61.80
Purchase #5	$37.27	10.318%	$41.1155	$41.12	$41.10	$41.10
Purchase #6	$191.30	9.731%	$209.9154	$209.92	$209.90	$209.90
Purchase #7	$89.68	3.109%	$92.4682	$92.47	$92.45	$92.50
7 purchase totals =	$814.56		$891.1214	$891.13	$891.05	$891.10