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	$121.73	5.405%	$128.3095	$128.31	$128.30	$128.30
Purchase #2	$123.50	13.309%	$139.9366	$139.94	$139.95	$139.90
Purchase #3	$118.55	7.521%	$127.4661	$127.47	$127.45	$127.50
Purchase #4	$145.42	4.534%	$152.0133	$152.01	$152.00	$152.00
Purchase #5	$136.42	7.346%	$146.4414	$146.44	$146.45	$146.40
Purchase #6	$203.43	11.743%	$227.3188	$227.32	$227.30	$227.30
Purchase #7	$139.35	3.803%	$144.6495	$144.65	$144.65	$144.60
7 purchase totals =	$988.40		$1,066.1352	$1,066.14	$1,066.10	$1,066.00