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	$70.87	10.445%	$78.2724	$78.27	$78.25	$78.30
Purchase #2	$238.93	9.369%	$261.3154	$261.32	$261.30	$261.30
Purchase #3	$29.36	13.786%	$33.4076	$33.41	$33.40	$33.40
Purchase #4	$75.46	4.607%	$78.9364	$78.94	$78.95	$78.90
Purchase #5	$228.65	3.847%	$237.4462	$237.45	$237.45	$237.40
Purchase #6	$105.81	7.443%	$113.6854	$113.69	$113.70	$113.70
Purchase #7	$97.43	11.479%	$108.614	$108.61	$108.60	$108.60
7 purchase totals =	$846.51		$911.6774	$911.69	$911.65	$911.60