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	$85.68	5.672%	$90.5398	$90.54	$90.55	$90.50
Purchase #2	$24.57	3.291%	$25.3786	$25.38	$25.40	$25.40
Purchase #3	$172.62	4.784%	$180.8781	$180.88	$180.90	$180.90
Purchase #4	$155.78	6.253%	$165.5209	$165.52	$165.50	$165.50
Purchase #5	$9.73	5.529%	$10.268	$10.27	$10.25	$10.30
Purchase #6	$91.86	8.750%	$99.8978	$99.90	$99.90	$99.90
Purchase #7	$26.40	9.694%	$28.9592	$28.96	$28.95	$29.00
7 purchase totals =	$566.64		$601.4424	$601.45	$601.45	$601.50