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	$20.26	6.459%	$21.5686	$21.57	$21.55	$21.60
Purchase #2	$187.80	4.818%	$196.8482	$196.85	$196.85	$196.80
Purchase #3	$38.31	8.599%	$41.6043	$41.60	$41.60	$41.60
Purchase #4	$138.64	3.680%	$143.742	$143.74	$143.75	$143.70
Purchase #5	$135.91	12.147%	$152.419	$152.42	$152.40	$152.40
Purchase #6	$121.45	4.819%	$127.3027	$127.30	$127.30	$127.30
Purchase #7	$149.66	12.554%	$168.4483	$168.45	$168.45	$168.40
7 purchase totals =	$792.03		$851.9331	$851.93	$851.90	$851.80