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	$96.59	12.842%	$108.9941	$108.99	$109.00	$109.00
Purchase #2	$160.88	5.761%	$170.1483	$170.15	$170.15	$170.10
Purchase #3	$109.77	4.727%	$114.9588	$114.96	$114.95	$115.00
Purchase #4	$104.61	7.106%	$112.0436	$112.04	$112.05	$112.00
Purchase #5	$145.68	4.829%	$152.7149	$152.71	$152.70	$152.70
Purchase #6	$72.57	13.671%	$82.491	$82.49	$82.50	$82.50
Purchase #7	$45.47	5.761%	$48.0895	$48.09	$48.10	$48.10
7 purchase totals =	$735.57		$789.4402	$789.43	$789.45	$789.40