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	$164.36	9.219%	$179.5123	$179.51	$179.50	$179.50
Purchase #2	$115.69	10.188%	$127.4765	$127.48	$127.50	$127.50
Purchase #3	$59.40	12.373%	$66.7496	$66.75	$66.75	$66.70
Purchase #4	$93.77	5.493%	$98.9208	$98.92	$98.90	$98.90
Purchase #5	$184.49	8.479%	$200.1329	$200.13	$200.15	$200.10
Purchase #6	$162.94	3.522%	$168.6787	$168.68	$168.70	$168.70
Purchase #7	$144.82	4.808%	$151.7829	$151.78	$151.80	$151.80
7 purchase totals =	$925.47		$993.2537	$993.25	$993.30	$993.20