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	$135.89	6.372%	$144.5489	$144.55	$144.55	$144.50
Purchase #2	$227.68	10.502%	$251.591	$251.59	$251.60	$251.60
Purchase #3	$137.99	5.175%	$145.131	$145.13	$145.15	$145.10
Purchase #4	$187.57	9.789%	$205.9312	$205.93	$205.95	$205.90
Purchase #5	$196.89	9.410%	$215.4173	$215.42	$215.40	$215.40
Purchase #6	$53.93	9.433%	$59.0172	$59.02	$59.00	$59.00
Purchase #7	$238.38	3.834%	$247.5195	$247.52	$247.50	$247.50
7 purchase totals =	$1,178.33		$1,269.1561	$1,269.16	$1,269.15	$1,269.00