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	$200.67	10.711%	$222.1638	$222.16	$222.15	$222.20
Purchase #2	$17.55	4.635%	$18.3634	$18.36	$18.35	$18.40
Purchase #3	$127.33	9.654%	$139.6224	$139.62	$139.60	$139.60
Purchase #4	$166.40	12.534%	$187.2566	$187.26	$187.25	$187.30
Purchase #5	$92.89	7.348%	$99.7156	$99.72	$99.70	$99.70
Purchase #6	$50.94	13.715%	$57.9264	$57.93	$57.95	$57.90
Purchase #7	$101.95	12.484%	$114.6774	$114.68	$114.70	$114.70
7 purchase totals =	$757.73		$839.7256	$839.73	$839.70	$839.80