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	$239.49	6.855%	$255.907	$255.91	$255.90	$255.90
Purchase #2	$63.28	11.679%	$70.6705	$70.67	$70.65	$70.70
Purchase #3	$100.85	4.694%	$105.5839	$105.58	$105.60	$105.60
Purchase #4	$179.86	5.347%	$189.4771	$189.48	$189.50	$189.50
Purchase #5	$221.64	10.794%	$245.5638	$245.56	$245.55	$245.60
Purchase #6	$74.79	7.678%	$80.5324	$80.53	$80.55	$80.50
Purchase #7	$221.56	13.477%	$251.4196	$251.42	$251.40	$251.40
7 purchase totals =	$1,101.47		$1,199.1543	$1,199.15	$1,199.15	$1,199.20