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	$159.56	3.537%	$165.2036	$165.20	$165.20	$165.20
Purchase #2	$172.26	7.258%	$184.7626	$184.76	$184.75	$184.80
Purchase #3	$78.86	5.139%	$82.9126	$82.91	$82.90	$82.90
Purchase #4	$187.82	11.465%	$209.3536	$209.35	$209.35	$209.40
Purchase #5	$126.83	4.235%	$132.2013	$132.20	$132.20	$132.20
Purchase #6	$42.52	10.726%	$47.0807	$47.08	$47.10	$47.10
Purchase #7	$67.47	6.868%	$72.1038	$72.10	$72.10	$72.10
7 purchase totals =	$835.32		$893.6182	$893.60	$893.60	$893.70