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	$58.89	13.171%	$66.6464	$66.65	$66.65	$66.60
Purchase #2	$29.57	9.572%	$32.4004	$32.40	$32.40	$32.40
Purchase #3	$40.36	11.620%	$45.0498	$45.05	$45.05	$45.00
Purchase #4	$220.77	7.125%	$236.4999	$236.50	$236.50	$236.50
Purchase #5	$245.46	13.788%	$279.304	$279.30	$279.30	$279.30
Purchase #6	$114.45	10.147%	$126.0632	$126.06	$126.05	$126.10
Purchase #7	$32.33	9.703%	$35.467	$35.47	$35.45	$35.50
7 purchase totals =	$741.83		$821.4307	$821.43	$821.40	$821.40