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	$96.43	3.738%	$100.0346	$100.03	$100.05	$100.00
Purchase #2	$164.72	12.247%	$184.8933	$184.89	$184.90	$184.90
Purchase #3	$178.39	6.762%	$190.4527	$190.45	$190.45	$190.50
Purchase #4	$50.41	3.438%	$52.1431	$52.14	$52.15	$52.10
Purchase #5	$106.32	4.851%	$111.4776	$111.48	$111.50	$111.50
Purchase #6	$220.78	3.241%	$227.9355	$227.94	$227.95	$227.90
Purchase #7	$94.90	6.809%	$101.3617	$101.36	$101.35	$101.40
7 purchase totals =	$911.95		$968.2985	$968.29	$968.35	$968.30