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	$41.66	11.539%	$46.4671	$46.47	$46.45	$46.50
Purchase #2	$57.61	6.660%	$61.4468	$61.45	$61.45	$61.40
Purchase #3	$40.77	3.727%	$42.2895	$42.29	$42.30	$42.30
Purchase #4	$136.69	10.319%	$150.795	$150.80	$150.80	$150.80
Purchase #5	$120.36	7.537%	$129.4315	$129.43	$129.45	$129.40
Purchase #6	$41.65	12.671%	$46.9275	$46.93	$46.95	$46.90
Purchase #7	$168.43	12.337%	$189.2092	$189.21	$189.20	$189.20
7 purchase totals =	$607.17		$666.5666	$666.58	$666.60	$666.50