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	$14.43	4.474%	$15.0756	$15.08	$15.10	$15.10
Purchase #2	$200.82	13.259%	$227.4467	$227.45	$227.45	$227.40
Purchase #3	$52.65	6.232%	$55.9311	$55.93	$55.95	$55.90
Purchase #4	$53.72	10.317%	$59.2623	$59.26	$59.25	$59.30
Purchase #5	$29.26	10.569%	$32.3525	$32.35	$32.35	$32.40
Purchase #6	$114.44	13.486%	$129.8734	$129.87	$129.85	$129.90
Purchase #7	$18.50	13.209%	$20.9437	$20.94	$20.95	$20.90
7 purchase totals =	$483.82		$540.8853	$540.88	$540.90	$540.90