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	$67.74	6.739%	$72.305	$72.31	$72.30	$72.30
Purchase #2	$239.56	6.865%	$256.0058	$256.01	$256.00	$256.00
Purchase #3	$127.83	8.702%	$138.9538	$138.95	$138.95	$139.00
Purchase #4	$39.39	13.241%	$44.6056	$44.61	$44.60	$44.60
Purchase #5	$43.55	13.571%	$49.4602	$49.46	$49.45	$49.50
Purchase #6	$205.59	11.832%	$229.9154	$229.92	$229.90	$229.90
Purchase #7	$89.58	10.258%	$98.7691	$98.77	$98.75	$98.80
7 purchase totals =	$813.24		$890.0149	$890.03	$889.95	$890.10