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	$115.47	7.128%	$123.7007	$123.70	$123.70	$123.70
Purchase #2	$154.35	11.434%	$171.9984	$172.00	$172.00	$172.00
Purchase #3	$83.77	10.309%	$92.4058	$92.41	$92.40	$92.40
Purchase #4	$86.77	4.282%	$90.4855	$90.49	$90.50	$90.50
Purchase #5	$57.25	7.591%	$61.5958	$61.60	$61.60	$61.60
Purchase #6	$186.68	12.540%	$210.0897	$210.09	$210.10	$210.10
Purchase #7	$101.54	3.708%	$105.3051	$105.31	$105.30	$105.30
7 purchase totals =	$785.83		$855.5810	$855.60	$855.60	$855.60