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	$87.43	13.866%	$99.553	$99.55	$99.55	$99.60
Purchase #2	$145.84	9.381%	$159.5213	$159.52	$159.50	$159.50
Purchase #3	$20.93	12.717%	$23.5917	$23.59	$23.60	$23.60
Purchase #4	$98.82	9.648%	$108.3542	$108.35	$108.35	$108.40
Purchase #5	$224.42	6.374%	$238.7245	$238.72	$238.70	$238.70
Purchase #6	$76.46	12.314%	$85.8753	$85.88	$85.90	$85.90
Purchase #7	$138.43	13.227%	$156.7401	$156.74	$156.75	$156.70
7 purchase totals =	$792.33		$872.3601	$872.35	$872.35	$872.40