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	$155.98	8.192%	$168.7579	$168.76	$168.75	$168.80
Purchase #2	$242.27	9.105%	$264.3287	$264.33	$264.35	$264.30
Purchase #3	$43.59	6.249%	$46.3139	$46.31	$46.30	$46.30
Purchase #4	$134.85	3.658%	$139.7828	$139.78	$139.80	$139.80
Purchase #5	$131.83	3.390%	$136.299	$136.30	$136.30	$136.30
Purchase #6	$183.83	3.717%	$190.663	$190.66	$190.65	$190.70
Purchase #7	$248.50	8.296%	$269.1156	$269.12	$269.10	$269.10
7 purchase totals =	$1,140.85		$1,215.2609	$1,215.26	$1,215.25	$1,215.30