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	$46.81	8.561%	$50.8174	$50.82	$50.80	$50.80
Purchase #2	$143.48	10.566%	$158.6401	$158.64	$158.65	$158.60
Purchase #3	$218.40	11.539%	$243.6012	$243.60	$243.60	$243.60
Purchase #4	$230.66	13.750%	$262.3758	$262.38	$262.40	$262.40
Purchase #5	$149.63	11.791%	$167.2729	$167.27	$167.25	$167.30
Purchase #6	$34.66	13.221%	$39.2424	$39.24	$39.25	$39.20
Purchase #7	$207.56	12.711%	$233.943	$233.94	$233.95	$233.90
7 purchase totals =	$1,031.20		$1,155.8928	$1,155.89	$1,155.90	$1,155.80