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	$11.80	10.136%	$12.996	$13.00	$13.00	$13.00
Purchase #2	$61.78	13.686%	$70.2352	$70.24	$70.25	$70.20
Purchase #3	$19.90	3.582%	$20.6128	$20.61	$20.60	$20.60
Purchase #4	$151.51	10.298%	$167.1125	$167.11	$167.10	$167.10
Purchase #5	$177.42	7.326%	$190.4178	$190.42	$190.40	$190.40
Purchase #6	$215.59	13.247%	$244.1492	$244.15	$244.15	$244.10
Purchase #7	$62.98	7.574%	$67.7501	$67.75	$67.75	$67.80
7 purchase totals =	$700.98		$773.2736	$773.28	$773.25	$773.20