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	$97.73	5.738%	$103.3377	$103.34	$103.35	$103.30
Purchase #2	$210.46	13.558%	$238.9942	$238.99	$239.00	$239.00
Purchase #3	$50.64	7.158%	$54.2648	$54.26	$54.25	$54.30
Purchase #4	$46.31	13.577%	$52.5975	$52.60	$52.60	$52.60
Purchase #5	$250.78	6.420%	$266.8801	$266.88	$266.90	$266.90
Purchase #6	$62.81	10.518%	$69.4164	$69.42	$69.40	$69.40
Purchase #7	$130.31	5.443%	$137.4028	$137.40	$137.40	$137.40
7 purchase totals =	$849.04		$922.8935	$922.89	$922.90	$922.90