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	$249.58	9.388%	$273.0106	$273.01	$273.00	$273.00
Purchase #2	$158.49	12.459%	$178.2363	$178.24	$178.25	$178.20
Purchase #3	$102.78	4.435%	$107.3383	$107.34	$107.35	$107.30
Purchase #4	$195.30	8.178%	$211.2716	$211.27	$211.25	$211.30
Purchase #5	$102.86	8.238%	$111.3336	$111.33	$111.35	$111.30
Purchase #6	$149.51	4.849%	$156.7597	$156.76	$156.75	$156.80
Purchase #7	$48.40	4.526%	$50.5906	$50.59	$50.60	$50.60
7 purchase totals =	$1,006.92		$1,088.5407	$1,088.54	$1,088.55	$1,088.50