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	$39.53	7.495%	$42.4928	$42.49	$42.50	$42.50
Purchase #2	$79.99	6.737%	$85.3789	$85.38	$85.40	$85.40
Purchase #3	$41.28	10.576%	$45.6458	$45.65	$45.65	$45.60
Purchase #4	$238.49	5.640%	$251.9408	$251.94	$251.95	$251.90
Purchase #5	$163.47	9.232%	$178.5616	$178.56	$178.55	$178.60
Purchase #6	$82.90	3.508%	$85.8081	$85.81	$85.80	$85.80
Purchase #7	$222.62	12.773%	$251.0553	$251.06	$251.05	$251.10
7 purchase totals =	$868.28		$940.8833	$940.89	$940.90	$940.90