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	$32.29	8.657%	$35.0853	$35.09	$35.10	$35.10
Purchase #2	$221.79	12.244%	$248.946	$248.95	$248.95	$248.90
Purchase #3	$163.94	4.403%	$171.1583	$171.16	$171.15	$171.20
Purchase #4	$68.69	6.132%	$72.9021	$72.90	$72.90	$72.90
Purchase #5	$26.92	10.187%	$29.6623	$29.66	$29.65	$29.70
Purchase #6	$54.36	13.180%	$61.5246	$61.52	$61.50	$61.50
Purchase #7	$44.77	3.134%	$46.1731	$46.17	$46.15	$46.20
7 purchase totals =	$612.76		$665.4517	$665.45	$665.40	$665.50