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	$185.48	7.382%	$199.1721	$199.17	$199.15	$199.20
Purchase #2	$89.55	3.432%	$92.6234	$92.62	$92.60	$92.60
Purchase #3	$238.90	11.168%	$265.5804	$265.58	$265.60	$265.60
Purchase #4	$174.59	3.242%	$180.2502	$180.25	$180.25	$180.30
Purchase #5	$168.25	4.156%	$175.2425	$175.24	$175.25	$175.20
Purchase #6	$17.97	11.741%	$20.0799	$20.08	$20.10	$20.10
Purchase #7	$116.86	13.291%	$132.3919	$132.39	$132.40	$132.40
7 purchase totals =	$991.60		$1,065.3404	$1,065.33	$1,065.35	$1,065.40