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	$13.54	11.249%	$15.0631	$15.06	$15.05	$15.10
Purchase #2	$72.91	13.147%	$82.4955	$82.50	$82.50	$82.50
Purchase #3	$157.67	11.776%	$176.2372	$176.24	$176.25	$176.20
Purchase #4	$15.28	7.526%	$16.43	$16.43	$16.45	$16.40
Purchase #5	$108.28	3.256%	$111.8056	$111.81	$111.80	$111.80
Purchase #6	$240.48	5.646%	$254.0575	$254.06	$254.05	$254.10
Purchase #7	$163.61	3.107%	$168.6934	$168.69	$168.70	$168.70
7 purchase totals =	$771.77		$824.7823	$824.79	$824.80	$824.80