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	$226.35	9.691%	$248.2856	$248.29	$248.30	$248.30
Purchase #2	$85.39	4.716%	$89.417	$89.42	$89.40	$89.40
Purchase #3	$122.57	11.848%	$137.0921	$137.09	$137.10	$137.10
Purchase #4	$210.85	13.188%	$238.6569	$238.66	$238.65	$238.70
Purchase #5	$235.73	4.260%	$245.7721	$245.77	$245.75	$245.80
Purchase #6	$37.80	13.266%	$42.8145	$42.81	$42.80	$42.80
Purchase #7	$139.25	10.150%	$153.3839	$153.38	$153.40	$153.40
7 purchase totals =	$1,057.94		$1,155.4221	$1,155.42	$1,155.40	$1,155.50