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	$167.85	6.632%	$178.9818	$178.98	$179.00	$179.00
Purchase #2	$82.83	8.385%	$89.7753	$89.78	$89.80	$89.80
Purchase #3	$242.63	6.767%	$259.0488	$259.05	$259.05	$259.00
Purchase #4	$111.64	13.802%	$127.0486	$127.05	$127.05	$127.00
Purchase #5	$244.51	5.461%	$257.8627	$257.86	$257.85	$257.90
Purchase #6	$183.38	7.436%	$197.0161	$197.02	$197.00	$197.00
Purchase #7	$106.85	10.356%	$117.9154	$117.92	$117.90	$117.90
7 purchase totals =	$1,139.69		$1,227.6487	$1,227.66	$1,227.65	$1,227.60