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	$224.96	6.195%	$238.8963	$238.90	$238.90	$238.90
Purchase #2	$93.33	3.401%	$96.5042	$96.50	$96.50	$96.50
Purchase #3	$48.26	5.390%	$50.8612	$50.86	$50.85	$50.90
Purchase #4	$51.77	5.519%	$54.6272	$54.63	$54.65	$54.60
Purchase #5	$40.28	12.777%	$45.4266	$45.43	$45.45	$45.40
Purchase #6	$128.25	12.571%	$144.3723	$144.37	$144.35	$144.40
Purchase #7	$187.91	9.219%	$205.2334	$205.23	$205.25	$205.20
7 purchase totals =	$774.76		$835.9212	$835.92	$835.95	$835.90