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	$92.75	8.588%	$100.7154	$100.72	$100.70	$100.70
Purchase #2	$83.84	8.873%	$91.2791	$91.28	$91.30	$91.30
Purchase #3	$115.55	10.367%	$127.5291	$127.53	$127.55	$127.50
Purchase #4	$178.25	11.487%	$198.7256	$198.73	$198.75	$198.70
Purchase #5	$78.87	10.866%	$87.44	$87.44	$87.45	$87.40
Purchase #6	$183.25	9.569%	$200.7852	$200.79	$200.80	$200.80
Purchase #7	$26.31	8.492%	$28.5442	$28.54	$28.55	$28.50
7 purchase totals =	$758.82		$835.0186	$835.03	$835.10	$834.90