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	$9.85	7.408%	$10.5797	$10.58	$10.60	$10.60
Purchase #2	$82.44	4.176%	$85.8827	$85.88	$85.90	$85.90
Purchase #3	$120.67	13.825%	$137.3526	$137.35	$137.35	$137.40
Purchase #4	$153.29	8.137%	$165.7632	$165.76	$165.75	$165.80
Purchase #5	$176.68	7.239%	$189.4699	$189.47	$189.45	$189.50
Purchase #6	$144.64	13.705%	$164.4629	$164.46	$164.45	$164.50
Purchase #7	$103.48	9.253%	$113.055	$113.06	$113.05	$113.10
7 purchase totals =	$791.05		$866.5660	$866.56	$866.55	$866.80