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	$65.48	5.110%	$68.826	$68.83	$68.85	$68.80
Purchase #2	$72.29	9.571%	$79.2089	$79.21	$79.20	$79.20
Purchase #3	$41.99	4.312%	$43.8006	$43.80	$43.80	$43.80
Purchase #4	$9.92	6.257%	$10.5407	$10.54	$10.55	$10.50
Purchase #5	$141.71	10.663%	$156.8205	$156.82	$156.80	$156.80
Purchase #6	$142.73	9.365%	$156.0967	$156.10	$156.10	$156.10
Purchase #7	$145.57	3.789%	$151.0856	$151.09	$151.10	$151.10
7 purchase totals =	$619.69		$666.3790	$666.39	$666.40	$666.30