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	$38.96	6.293%	$41.4118	$41.41	$41.40	$41.40
Purchase #2	$153.97	9.113%	$168.0013	$168.00	$168.00	$168.00
Purchase #3	$18.77	5.144%	$19.7355	$19.74	$19.75	$19.70
Purchase #4	$185.52	10.795%	$205.5469	$205.55	$205.55	$205.50
Purchase #5	$37.81	12.432%	$42.5105	$42.51	$42.50	$42.50
Purchase #6	$155.44	8.498%	$168.6493	$168.65	$168.65	$168.60
Purchase #7	$26.82	9.674%	$29.4146	$29.41	$29.40	$29.40
7 purchase totals =	$617.29		$675.2699	$675.27	$675.25	$675.10