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	$33.25	3.492%	$34.4111	$34.41	$34.40	$34.40
Purchase #2	$73.90	12.546%	$83.1715	$83.17	$83.15	$83.20
Purchase #3	$11.52	11.451%	$12.8392	$12.84	$12.85	$12.80
Purchase #4	$79.61	3.631%	$82.5006	$82.50	$82.50	$82.50
Purchase #5	$121.89	5.711%	$128.8511	$128.85	$128.85	$128.90
Purchase #6	$189.83	7.728%	$204.5001	$204.50	$204.50	$204.50
Purchase #7	$125.94	10.681%	$139.3917	$139.39	$139.40	$139.40
7 purchase totals =	$635.94		$685.6653	$685.66	$685.65	$685.70