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	$45.90	7.701%	$49.4348	$49.43	$49.45	$49.40
Purchase #2	$15.94	13.517%	$18.0946	$18.09	$18.10	$18.10
Purchase #3	$94.83	11.129%	$105.3836	$105.38	$105.40	$105.40
Purchase #4	$219.72	11.163%	$244.2473	$244.25	$244.25	$244.20
Purchase #5	$122.91	12.657%	$138.4667	$138.47	$138.45	$138.50
Purchase #6	$182.56	9.830%	$200.5056	$200.51	$200.50	$200.50
Purchase #7	$72.27	11.623%	$80.6699	$80.67	$80.65	$80.70
7 purchase totals =	$754.13		$836.8025	$836.80	$836.80	$836.80