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	$25.92	6.140%	$27.5115	$27.51	$27.50	$27.50
Purchase #2	$170.53	12.178%	$191.2971	$191.30	$191.30	$191.30
Purchase #3	$138.86	11.611%	$154.983	$154.98	$155.00	$155.00
Purchase #4	$242.69	7.257%	$260.302	$260.30	$260.30	$260.30
Purchase #5	$36.47	7.252%	$39.1148	$39.11	$39.10	$39.10
Purchase #6	$53.86	9.793%	$59.1345	$59.13	$59.15	$59.10
Purchase #7	$162.68	4.667%	$170.2723	$170.27	$170.25	$170.30
7 purchase totals =	$831.01		$902.6152	$902.60	$902.60	$902.60