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	$192.35	6.139%	$204.1584	$204.16	$204.15	$204.20
Purchase #2	$14.54	8.510%	$15.7774	$15.78	$15.80	$15.80
Purchase #3	$49.37	4.772%	$51.7259	$51.73	$51.75	$51.70
Purchase #4	$122.58	11.268%	$136.3923	$136.39	$136.40	$136.40
Purchase #5	$75.66	9.568%	$82.8991	$82.90	$82.90	$82.90
Purchase #6	$86.88	5.359%	$91.5359	$91.54	$91.55	$91.50
Purchase #7	$41.33	9.783%	$45.3733	$45.37	$45.35	$45.40
7 purchase totals =	$582.71		$627.8623	$627.87	$627.90	$627.90