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	$190.74	5.160%	$200.5822	$200.58	$200.60	$200.60
Purchase #2	$219.75	9.204%	$239.9758	$239.98	$240.00	$240.00
Purchase #3	$108.75	10.305%	$119.9567	$119.96	$119.95	$120.00
Purchase #4	$81.34	11.336%	$90.5607	$90.56	$90.55	$90.60
Purchase #5	$65.91	6.590%	$70.2535	$70.25	$70.25	$70.30
Purchase #6	$217.52	12.325%	$244.3293	$244.33	$244.35	$244.30
Purchase #7	$28.51	10.168%	$31.4089	$31.41	$31.40	$31.40
7 purchase totals =	$912.52		$997.0671	$997.07	$997.10	$997.20