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	$153.56	4.470%	$160.4241	$160.42	$160.40	$160.40
Purchase #2	$167.53	12.502%	$188.4746	$188.47	$188.45	$188.50
Purchase #3	$5.88	6.667%	$6.272	$6.27	$6.25	$6.30
Purchase #4	$111.78	4.791%	$117.1354	$117.14	$117.15	$117.10
Purchase #5	$184.99	11.526%	$206.3119	$206.31	$206.30	$206.30
Purchase #6	$188.76	9.534%	$206.7564	$206.76	$206.75	$206.80
Purchase #7	$83.39	7.115%	$89.3232	$89.32	$89.30	$89.30
7 purchase totals =	$895.89		$974.6976	$974.69	$974.60	$974.70