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	$39.69	5.763%	$41.9773	$41.98	$42.00	$42.00
Purchase #2	$9.58	11.235%	$10.6563	$10.66	$10.65	$10.70
Purchase #3	$59.65	7.194%	$63.9412	$63.94	$63.95	$63.90
Purchase #4	$187.43	3.578%	$194.1362	$194.14	$194.15	$194.10
Purchase #5	$40.30	5.845%	$42.6555	$42.66	$42.65	$42.70
Purchase #6	$67.55	7.223%	$72.4291	$72.43	$72.45	$72.40
Purchase #7	$185.76	7.313%	$199.3446	$199.34	$199.35	$199.30
7 purchase totals =	$589.96		$625.1402	$625.15	$625.20	$625.10