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	$128.31	8.356%	$139.0316	$139.03	$139.05	$139.00
Purchase #2	$233.92	5.791%	$247.4663	$247.47	$247.45	$247.50
Purchase #3	$110.95	11.296%	$123.4829	$123.48	$123.50	$123.50
Purchase #4	$127.45	13.312%	$144.4161	$144.42	$144.40	$144.40
Purchase #5	$33.83	10.367%	$37.3372	$37.34	$37.35	$37.30
Purchase #6	$179.43	4.121%	$186.8243	$186.82	$186.80	$186.80
Purchase #7	$59.64	11.625%	$66.5732	$66.57	$66.55	$66.60
7 purchase totals =	$873.53		$945.1316	$945.13	$945.10	$945.10