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	$99.77	9.739%	$109.4866	$109.49	$109.50	$109.50
Purchase #2	$61.33	7.653%	$66.0236	$66.02	$66.00	$66.00
Purchase #3	$229.75	11.360%	$255.8496	$255.85	$255.85	$255.80
Purchase #4	$95.62	13.265%	$108.304	$108.30	$108.30	$108.30
Purchase #5	$112.26	13.658%	$127.5925	$127.59	$127.60	$127.60
Purchase #6	$179.40	4.653%	$187.7475	$187.75	$187.75	$187.70
Purchase #7	$237.56	9.254%	$259.5438	$259.54	$259.55	$259.50
7 purchase totals =	$1,015.69		$1,114.5476	$1,114.54	$1,114.55	$1,114.40