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	$109.91	8.655%	$119.4227	$119.42	$119.40	$119.40
Purchase #2	$62.64	12.247%	$70.3115	$70.31	$70.30	$70.30
Purchase #3	$107.41	4.528%	$112.2735	$112.27	$112.25	$112.30
Purchase #4	$128.40	8.715%	$139.5901	$139.59	$139.60	$139.60
Purchase #5	$160.97	7.228%	$172.6049	$172.60	$172.60	$172.60
Purchase #6	$155.37	7.657%	$167.2667	$167.27	$167.25	$167.30
Purchase #7	$88.45	8.633%	$96.0859	$96.09	$96.10	$96.10
7 purchase totals =	$813.15		$877.5553	$877.55	$877.50	$877.60