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	$226.38	10.779%	$250.7815	$250.78	$250.80	$250.80
Purchase #2	$56.34	5.866%	$59.6449	$59.64	$59.65	$59.60
Purchase #3	$192.75	11.725%	$215.3499	$215.35	$215.35	$215.30
Purchase #4	$57.83	3.368%	$59.7777	$59.78	$59.80	$59.80
Purchase #5	$67.69	10.744%	$74.9626	$74.96	$74.95	$75.00
Purchase #6	$102.34	8.872%	$111.4196	$111.42	$111.40	$111.40
Purchase #7	$242.56	3.492%	$251.0302	$251.03	$251.05	$251.00
7 purchase totals =	$945.89		$1,022.9664	$1,022.96	$1,023.00	$1,022.90