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	$115.43	4.195%	$120.2723	$120.27	$120.25	$120.30
Purchase #2	$111.92	10.730%	$123.929	$123.93	$123.95	$123.90
Purchase #3	$241.98	7.329%	$259.7147	$259.71	$259.70	$259.70
Purchase #4	$29.80	6.391%	$31.7045	$31.70	$31.70	$31.70
Purchase #5	$142.77	10.209%	$157.3454	$157.35	$157.35	$157.30
Purchase #6	$70.60	10.506%	$78.0172	$78.02	$78.00	$78.00
Purchase #7	$244.60	8.151%	$264.5373	$264.54	$264.55	$264.50
7 purchase totals =	$957.10		$1,035.5204	$1,035.52	$1,035.50	$1,035.40