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	$112.55	9.450%	$123.186	$123.19	$123.20	$123.20
Purchase #2	$188.33	13.317%	$213.4099	$213.41	$213.40	$213.40
Purchase #3	$99.78	4.854%	$104.6233	$104.62	$104.60	$104.60
Purchase #4	$42.27	9.593%	$46.325	$46.33	$46.35	$46.30
Purchase #5	$133.38	9.180%	$145.6243	$145.62	$145.60	$145.60
Purchase #6	$50.68	4.320%	$52.8694	$52.87	$52.85	$52.90
Purchase #7	$49.26	9.693%	$54.0348	$54.03	$54.05	$54.00
7 purchase totals =	$676.25		$740.0727	$740.07	$740.05	$740.00