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	$31.98	5.495%	$33.7373	$33.74	$33.75	$33.70
Purchase #2	$29.67	4.826%	$31.1019	$31.10	$31.10	$31.10
Purchase #3	$211.27	13.406%	$239.5929	$239.59	$239.60	$239.60
Purchase #4	$137.85	10.614%	$152.4814	$152.48	$152.50	$152.50
Purchase #5	$182.65	13.857%	$207.9598	$207.96	$207.95	$208.00
Purchase #6	$90.72	13.731%	$103.1768	$103.18	$103.20	$103.20
Purchase #7	$45.51	6.276%	$48.3662	$48.37	$48.35	$48.40
7 purchase totals =	$729.65		$816.4163	$816.42	$816.45	$816.50