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	$11.34	12.651%	$12.7746	$12.77	$12.75	$12.80
Purchase #2	$192.70	7.766%	$207.6651	$207.67	$207.65	$207.70
Purchase #3	$33.76	10.282%	$37.2312	$37.23	$37.25	$37.20
Purchase #4	$186.86	5.104%	$196.3973	$196.40	$196.40	$196.40
Purchase #5	$230.82	12.223%	$259.0331	$259.03	$259.05	$259.00
Purchase #6	$225.38	3.388%	$233.0159	$233.02	$233.00	$233.00
Purchase #7	$51.85	4.869%	$54.3746	$54.37	$54.35	$54.40
7 purchase totals =	$932.71		$1,000.4918	$1,000.49	$1,000.45	$1,000.50