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	$248.76	10.117%	$273.927	$273.93	$273.95	$273.90
Purchase #2	$134.37	12.429%	$151.0708	$151.07	$151.05	$151.10
Purchase #3	$103.39	9.797%	$113.5191	$113.52	$113.50	$113.50
Purchase #4	$131.27	11.109%	$145.8528	$145.85	$145.85	$145.90
Purchase #5	$103.53	4.668%	$108.3628	$108.36	$108.35	$108.40
Purchase #6	$132.41	9.418%	$144.8804	$144.88	$144.90	$144.90
Purchase #7	$238.52	4.591%	$249.4705	$249.47	$249.45	$249.50
7 purchase totals =	$1,092.25		$1,187.0834	$1,187.08	$1,187.05	$1,187.20