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	$102.80	3.630%	$106.5316	$106.53	$106.55	$106.50
Purchase #2	$91.43	8.572%	$99.2674	$99.27	$99.25	$99.30
Purchase #3	$23.85	7.787%	$25.7072	$25.71	$25.70	$25.70
Purchase #4	$233.26	11.208%	$259.4038	$259.40	$259.40	$259.40
Purchase #5	$229.46	5.719%	$242.5828	$242.58	$242.60	$242.60
Purchase #6	$30.54	4.405%	$31.8853	$31.89	$31.90	$31.90
Purchase #7	$21.49	12.255%	$24.1236	$24.12	$24.10	$24.10
7 purchase totals =	$732.83		$789.5017	$789.50	$789.50	$789.50