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	$22.67	9.728%	$24.8753	$24.88	$24.90	$24.90
Purchase #2	$172.68	5.372%	$181.9564	$181.96	$181.95	$182.00
Purchase #3	$144.72	8.375%	$156.8403	$156.84	$156.85	$156.80
Purchase #4	$72.40	5.703%	$76.529	$76.53	$76.55	$76.50
Purchase #5	$79.35	13.144%	$89.7798	$89.78	$89.80	$89.80
Purchase #6	$166.89	4.181%	$173.8677	$173.87	$173.85	$173.90
Purchase #7	$18.70	4.736%	$19.5856	$19.59	$19.60	$19.60
7 purchase totals =	$677.41		$723.4341	$723.45	$723.50	$723.50