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	$250.66	8.851%	$272.8459	$272.85	$272.85	$272.80
Purchase #2	$229.32	6.575%	$244.3978	$244.40	$244.40	$244.40
Purchase #3	$149.42	12.493%	$168.087	$168.09	$168.10	$168.10
Purchase #4	$178.33	11.809%	$199.389	$199.39	$199.40	$199.40
Purchase #5	$54.52	4.575%	$57.0143	$57.01	$57.00	$57.00
Purchase #6	$238.76	7.166%	$255.8695	$255.87	$255.85	$255.90
Purchase #7	$24.29	3.247%	$25.0787	$25.08	$25.10	$25.10
7 purchase totals =	$1,125.30		$1,222.6822	$1,222.69	$1,222.70	$1,222.70