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	$246.76	8.838%	$268.5686	$268.57	$268.55	$268.60
Purchase #2	$168.97	4.581%	$176.7105	$176.71	$176.70	$176.70
Purchase #3	$228.51	11.414%	$254.5921	$254.59	$254.60	$254.60
Purchase #4	$137.46	9.477%	$150.4871	$150.49	$150.50	$150.50
Purchase #5	$42.49	4.752%	$44.5091	$44.51	$44.50	$44.50
Purchase #6	$175.78	8.362%	$190.4787	$190.48	$190.50	$190.50
Purchase #7	$49.91	4.435%	$52.1235	$52.12	$52.10	$52.10
7 purchase totals =	$1,049.88		$1,137.4696	$1,137.47	$1,137.45	$1,137.50