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	$104.99	6.582%	$111.9004	$111.90	$111.90	$111.90
Purchase #2	$115.97	5.552%	$122.4087	$122.41	$122.40	$122.40
Purchase #3	$33.99	4.706%	$35.5896	$35.59	$35.60	$35.60
Purchase #4	$29.31	12.726%	$33.04	$33.04	$33.05	$33.00
Purchase #5	$96.90	6.329%	$103.0328	$103.03	$103.05	$103.00
Purchase #6	$191.57	6.706%	$204.4167	$204.42	$204.40	$204.40
Purchase #7	$149.30	11.520%	$166.4994	$166.50	$166.50	$166.50
7 purchase totals =	$722.03		$776.8876	$776.89	$776.90	$776.80