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	$23.88	8.621%	$25.9387	$25.94	$25.95	$25.90
Purchase #2	$96.48	9.369%	$105.5192	$105.52	$105.50	$105.50
Purchase #3	$98.69	4.747%	$103.3748	$103.37	$103.35	$103.40
Purchase #4	$49.72	12.604%	$55.9867	$55.99	$56.00	$56.00
Purchase #5	$29.27	12.532%	$32.9381	$32.94	$32.95	$32.90
Purchase #6	$159.95	4.656%	$167.3973	$167.40	$167.40	$167.40
Purchase #7	$136.69	5.732%	$144.5251	$144.53	$144.55	$144.50
7 purchase totals =	$594.68		$635.6799	$635.69	$635.70	$635.60