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	$226.55	13.260%	$256.5905	$256.59	$256.60	$256.60
Purchase #2	$152.73	5.738%	$161.4936	$161.49	$161.50	$161.50
Purchase #3	$114.61	10.456%	$126.5936	$126.59	$126.60	$126.60
Purchase #4	$145.61	7.480%	$156.5016	$156.50	$156.50	$156.50
Purchase #5	$99.90	9.842%	$109.7322	$109.73	$109.75	$109.70
Purchase #6	$22.97	8.328%	$24.8829	$24.88	$24.90	$24.90
Purchase #7	$94.89	5.631%	$100.2333	$100.23	$100.25	$100.20
7 purchase totals =	$857.26		$936.0277	$936.01	$936.10	$936.00