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	$9.30	10.333%	$10.261	$10.26	$10.25	$10.30
Purchase #2	$220.30	12.798%	$248.494	$248.49	$248.50	$248.50
Purchase #3	$215.66	6.302%	$229.2509	$229.25	$229.25	$229.30
Purchase #4	$127.33	7.481%	$136.8556	$136.86	$136.85	$136.90
Purchase #5	$19.55	5.833%	$20.6904	$20.69	$20.70	$20.70
Purchase #6	$33.40	10.799%	$37.0069	$37.01	$37.00	$37.00
Purchase #7	$93.47	11.586%	$104.2994	$104.30	$104.30	$104.30
7 purchase totals =	$719.01		$786.8582	$786.86	$786.85	$787.00