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	$250.63	13.429%	$284.2871	$284.29	$284.30	$284.30
Purchase #2	$142.87	6.338%	$151.9251	$151.93	$151.95	$151.90
Purchase #3	$244.57	12.142%	$274.2657	$274.27	$274.25	$274.30
Purchase #4	$189.32	4.437%	$197.7201	$197.72	$197.70	$197.70
Purchase #5	$56.50	6.278%	$60.0471	$60.05	$60.05	$60.00
Purchase #6	$10.50	3.808%	$10.8998	$10.90	$10.90	$10.90
Purchase #7	$233.77	3.705%	$242.4312	$242.43	$242.45	$242.40
7 purchase totals =	$1,128.16		$1,221.5761	$1,221.59	$1,221.60	$1,221.50