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	$76.75	4.259%	$80.0188	$80.02	$80.00	$80.00
Purchase #2	$18.83	12.311%	$21.1482	$21.15	$21.15	$21.10
Purchase #3	$127.34	3.464%	$131.7511	$131.75	$131.75	$131.80
Purchase #4	$24.66	11.556%	$27.5097	$27.51	$27.50	$27.50
Purchase #5	$12.70	6.207%	$13.4883	$13.49	$13.50	$13.50
Purchase #6	$82.48	8.179%	$89.226	$89.23	$89.25	$89.20
Purchase #7	$94.86	5.711%	$100.2775	$100.28	$100.30	$100.30
7 purchase totals =	$437.62		$463.4196	$463.43	$463.45	$463.40