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	$211.25	8.648%	$229.5189	$229.52	$229.50	$229.50
Purchase #2	$237.48	8.119%	$256.761	$256.76	$256.75	$256.80
Purchase #3	$125.83	10.440%	$138.9667	$138.97	$138.95	$139.00
Purchase #4	$163.51	11.392%	$182.1371	$182.14	$182.15	$182.10
Purchase #5	$138.32	9.485%	$151.4397	$151.44	$151.45	$151.40
Purchase #6	$168.60	4.359%	$175.9493	$175.95	$175.95	$175.90
Purchase #7	$34.41	8.437%	$37.3132	$37.31	$37.30	$37.30
7 purchase totals =	$1,079.40		$1,172.0859	$1,172.09	$1,172.05	$1,172.00