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	$153.44	9.734%	$168.3758	$168.38	$168.40	$168.40
Purchase #2	$225.71	11.204%	$250.9985	$251.00	$251.00	$251.00
Purchase #3	$21.86	11.798%	$24.439	$24.44	$24.45	$24.40
Purchase #4	$96.28	7.237%	$103.2478	$103.25	$103.25	$103.20
Purchase #5	$214.96	6.262%	$228.4208	$228.42	$228.40	$228.40
Purchase #6	$39.72	4.423%	$41.4768	$41.48	$41.50	$41.50
Purchase #7	$18.32	13.803%	$20.8487	$20.85	$20.85	$20.80
7 purchase totals =	$770.29		$837.8074	$837.82	$837.85	$837.70