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	$96.55	3.578%	$100.0046	$100.00	$100.00	$100.00
Purchase #2	$118.53	13.555%	$134.5967	$134.60	$134.60	$134.60
Purchase #3	$158.90	10.461%	$175.5225	$175.52	$175.50	$175.50
Purchase #4	$159.63	11.681%	$178.2764	$178.28	$178.30	$178.30
Purchase #5	$145.94	13.621%	$165.8185	$165.82	$165.80	$165.80
Purchase #6	$145.32	5.192%	$152.865	$152.87	$152.85	$152.90
Purchase #7	$23.77	6.560%	$25.3293	$25.33	$25.35	$25.30
7 purchase totals =	$848.64		$932.4130	$932.42	$932.40	$932.40