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	$28.62	4.462%	$29.897	$29.90	$29.90	$29.90
Purchase #2	$86.30	7.161%	$92.4799	$92.48	$92.50	$92.50
Purchase #3	$175.76	11.781%	$196.4663	$196.47	$196.45	$196.50
Purchase #4	$48.82	5.455%	$51.4831	$51.48	$51.50	$51.50
Purchase #5	$163.78	9.627%	$179.5471	$179.55	$179.55	$179.50
Purchase #6	$24.89	8.616%	$27.0345	$27.03	$27.05	$27.00
Purchase #7	$228.54	6.620%	$243.6693	$243.67	$243.65	$243.70
7 purchase totals =	$756.71		$820.5772	$820.58	$820.60	$820.60