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	$223.25	4.631%	$233.5887	$233.59	$233.60	$233.60
Purchase #2	$114.35	4.871%	$119.92	$119.92	$119.90	$119.90
Purchase #3	$180.89	6.202%	$192.1088	$192.11	$192.10	$192.10
Purchase #4	$224.97	3.653%	$233.1882	$233.19	$233.20	$233.20
Purchase #5	$242.86	8.516%	$263.542	$263.54	$263.55	$263.50
Purchase #6	$19.62	11.366%	$21.85	$21.85	$21.85	$21.90
Purchase #7	$46.66	13.374%	$52.9003	$52.90	$52.90	$52.90
7 purchase totals =	$1,052.60		$1,117.0980	$1,117.10	$1,117.10	$1,117.10