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	$102.67	7.499%	$110.3692	$110.37	$110.35	$110.40
Purchase #2	$93.89	5.598%	$99.146	$99.15	$99.15	$99.10
Purchase #3	$41.43	6.245%	$44.0173	$44.02	$44.00	$44.00
Purchase #4	$103.53	10.247%	$114.1387	$114.14	$114.15	$114.10
Purchase #5	$219.89	6.289%	$233.7189	$233.72	$233.70	$233.70
Purchase #6	$70.53	12.565%	$79.3921	$79.39	$79.40	$79.40
Purchase #7	$145.51	5.705%	$153.8113	$153.81	$153.80	$153.80
7 purchase totals =	$777.45		$834.5935	$834.60	$834.55	$834.50