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	$173.64	7.670%	$186.9582	$186.96	$186.95	$187.00
Purchase #2	$119.86	13.712%	$136.2952	$136.30	$136.30	$136.30
Purchase #3	$151.42	10.679%	$167.5901	$167.59	$167.60	$167.60
Purchase #4	$108.37	10.285%	$119.5159	$119.52	$119.50	$119.50
Purchase #5	$31.37	6.229%	$33.324	$33.32	$33.30	$33.30
Purchase #6	$129.50	7.546%	$139.2721	$139.27	$139.25	$139.30
Purchase #7	$127.93	6.624%	$136.4041	$136.40	$136.40	$136.40
7 purchase totals =	$842.09		$919.3596	$919.36	$919.30	$919.40