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	$101.47	13.279%	$114.9442	$114.94	$114.95	$114.90
Purchase #2	$104.65	3.707%	$108.5294	$108.53	$108.55	$108.50
Purchase #3	$34.67	11.335%	$38.5998	$38.60	$38.60	$38.60
Purchase #4	$152.48	9.228%	$166.5509	$166.55	$166.55	$166.60
Purchase #5	$95.98	9.636%	$105.2286	$105.23	$105.25	$105.20
Purchase #6	$74.41	9.571%	$81.5318	$81.53	$81.55	$81.50
Purchase #7	$189.67	5.526%	$200.1512	$200.15	$200.15	$200.20
7 purchase totals =	$753.33		$815.5359	$815.53	$815.60	$815.50