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	$24.49	3.232%	$25.2815	$25.28	$25.30	$25.30
Purchase #2	$164.98	11.856%	$184.54	$184.54	$184.55	$184.50
Purchase #3	$72.71	6.504%	$77.4391	$77.44	$77.45	$77.40
Purchase #4	$110.72	11.529%	$123.4849	$123.48	$123.50	$123.50
Purchase #5	$190.83	3.435%	$197.385	$197.39	$197.40	$197.40
Purchase #6	$146.65	13.108%	$165.8729	$165.87	$165.85	$165.90
Purchase #7	$20.50	11.278%	$22.812	$22.81	$22.80	$22.80
7 purchase totals =	$730.88		$796.8154	$796.81	$796.85	$796.80