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	$128.37	11.855%	$143.5883	$143.59	$143.60	$143.60
Purchase #2	$50.30	4.480%	$52.5534	$52.55	$52.55	$52.60
Purchase #3	$129.63	13.783%	$147.4969	$147.50	$147.50	$147.50
Purchase #4	$98.86	9.751%	$108.4998	$108.50	$108.50	$108.50
Purchase #5	$155.44	3.492%	$160.868	$160.87	$160.85	$160.90
Purchase #6	$92.61	13.825%	$105.4133	$105.41	$105.40	$105.40
Purchase #7	$66.56	12.803%	$75.0817	$75.08	$75.10	$75.10
7 purchase totals =	$721.77		$793.5014	$793.50	$793.50	$793.60