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	$248.81	8.866%	$270.8695	$270.87	$270.85	$270.90
Purchase #2	$241.63	7.369%	$259.4357	$259.44	$259.45	$259.40
Purchase #3	$11.80	8.756%	$12.8332	$12.83	$12.85	$12.80
Purchase #4	$180.90	4.129%	$188.3694	$188.37	$188.35	$188.40
Purchase #5	$20.31	11.790%	$22.7045	$22.70	$22.70	$22.70
Purchase #6	$157.35	9.525%	$172.3376	$172.34	$172.35	$172.30
Purchase #7	$138.83	4.323%	$144.8316	$144.83	$144.85	$144.80
7 purchase totals =	$999.63		$1,071.3815	$1,071.38	$1,071.40	$1,071.30