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	$139.84	7.579%	$150.4385	$150.44	$150.45	$150.40
Purchase #2	$132.66	8.816%	$144.3553	$144.36	$144.35	$144.40
Purchase #3	$104.28	5.282%	$109.7881	$109.79	$109.80	$109.80
Purchase #4	$113.72	12.422%	$127.8463	$127.85	$127.85	$127.80
Purchase #5	$125.52	3.705%	$130.1705	$130.17	$130.15	$130.20
Purchase #6	$28.65	11.335%	$31.8975	$31.90	$31.90	$31.90
Purchase #7	$9.67	13.803%	$11.0048	$11.00	$11.00	$11.00
7 purchase totals =	$654.34		$705.5010	$705.51	$705.50	$705.50