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	$37.93	8.499%	$41.1537	$41.15	$41.15	$41.20
Purchase #2	$130.83	5.870%	$138.5097	$138.51	$138.50	$138.50
Purchase #3	$127.87	10.474%	$141.2631	$141.26	$141.25	$141.30
Purchase #4	$151.96	12.412%	$170.8213	$170.82	$170.80	$170.80
Purchase #5	$112.48	9.479%	$123.142	$123.14	$123.15	$123.10
Purchase #6	$223.25	11.591%	$249.1269	$249.13	$249.15	$249.10
Purchase #7	$19.50	7.544%	$20.9711	$20.97	$20.95	$21.00
7 purchase totals =	$803.82		$884.9878	$884.98	$884.95	$885.00