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	$99.81	13.222%	$113.0069	$113.01	$113.00	$113.00
Purchase #2	$95.45	13.529%	$108.3634	$108.36	$108.35	$108.40
Purchase #3	$50.71	4.427%	$52.9549	$52.95	$52.95	$53.00
Purchase #4	$238.79	13.741%	$271.6021	$271.60	$271.60	$271.60
Purchase #5	$49.92	7.373%	$53.6006	$53.60	$53.60	$53.60
Purchase #6	$20.87	3.504%	$21.6013	$21.60	$21.60	$21.60
Purchase #7	$36.96	6.152%	$39.2338	$39.23	$39.25	$39.20
7 purchase totals =	$592.51		$660.3630	$660.35	$660.35	$660.40