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	$191.49	4.387%	$199.8907	$199.89	$199.90	$199.90
Purchase #2	$47.78	11.848%	$53.441	$53.44	$53.45	$53.40
Purchase #3	$55.26	8.309%	$59.8516	$59.85	$59.85	$59.90
Purchase #4	$107.34	10.229%	$118.3198	$118.32	$118.30	$118.30
Purchase #5	$19.32	9.117%	$21.0814	$21.08	$21.10	$21.10
Purchase #6	$53.55	13.150%	$60.5918	$60.59	$60.60	$60.60
Purchase #7	$133.25	3.472%	$137.8764	$137.88	$137.90	$137.90
7 purchase totals =	$607.99		$651.0527	$651.05	$651.10	$651.10