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	$33.45	13.370%	$37.9223	$37.92	$37.90	$37.90
Purchase #2	$221.90	12.541%	$249.7285	$249.73	$249.75	$249.70
Purchase #3	$193.82	5.812%	$205.0848	$205.08	$205.10	$205.10
Purchase #4	$248.40	12.438%	$279.296	$279.30	$279.30	$279.30
Purchase #5	$82.87	7.874%	$89.3952	$89.40	$89.40	$89.40
Purchase #6	$196.76	13.778%	$223.8696	$223.87	$223.85	$223.90
Purchase #7	$181.42	5.178%	$190.8139	$190.81	$190.80	$190.80
7 purchase totals =	$1,158.62		$1,276.1103	$1,276.11	$1,276.10	$1,276.10