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	$48.43	13.668%	$55.0494	$55.05	$55.05	$55.00
Purchase #2	$57.49	3.538%	$59.524	$59.52	$59.50	$59.50
Purchase #3	$83.27	7.398%	$89.4303	$89.43	$89.45	$89.40
Purchase #4	$148.77	10.773%	$164.797	$164.80	$164.80	$164.80
Purchase #5	$118.61	3.223%	$122.4328	$122.43	$122.45	$122.40
Purchase #6	$92.28	5.541%	$97.3932	$97.39	$97.40	$97.40
Purchase #7	$200.95	7.637%	$216.2966	$216.30	$216.30	$216.30
7 purchase totals =	$749.80		$804.9233	$804.92	$804.95	$804.80