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	$241.78	13.113%	$273.4846	$273.48	$273.50	$273.50
Purchase #2	$126.95	10.670%	$140.4956	$140.50	$140.50	$140.50
Purchase #3	$34.96	13.267%	$39.5981	$39.60	$39.60	$39.60
Purchase #4	$48.72	5.297%	$51.3007	$51.30	$51.30	$51.30
Purchase #5	$116.64	10.477%	$128.8604	$128.86	$128.85	$128.90
Purchase #6	$179.49	6.270%	$190.744	$190.74	$190.75	$190.70
Purchase #7	$47.39	5.765%	$50.122	$50.12	$50.10	$50.10
7 purchase totals =	$795.93		$874.6054	$874.60	$874.60	$874.60