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	$26.60	13.703%	$30.245	$30.25	$30.25	$30.20
Purchase #2	$34.89	3.720%	$36.1879	$36.19	$36.20	$36.20
Purchase #3	$144.87	5.245%	$152.4684	$152.47	$152.45	$152.50
Purchase #4	$113.86	13.803%	$129.5761	$129.58	$129.60	$129.60
Purchase #5	$181.80	3.401%	$187.983	$187.98	$188.00	$188.00
Purchase #6	$72.73	13.663%	$82.6671	$82.67	$82.65	$82.70
Purchase #7	$40.95	10.508%	$45.253	$45.25	$45.25	$45.30
7 purchase totals =	$615.70		$664.3805	$664.39	$664.40	$664.50