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	$241.89	5.839%	$256.014	$256.01	$256.00	$256.00
Purchase #2	$214.85	10.503%	$237.4157	$237.42	$237.40	$237.40
Purchase #3	$236.61	8.418%	$256.5278	$256.53	$256.55	$256.50
Purchase #4	$48.76	10.451%	$53.8559	$53.86	$53.85	$53.90
Purchase #5	$20.55	9.790%	$22.5618	$22.56	$22.55	$22.60
Purchase #6	$100.54	7.155%	$107.7336	$107.73	$107.75	$107.70
Purchase #7	$156.57	11.662%	$174.8292	$174.83	$174.85	$174.80
7 purchase totals =	$1,019.77		$1,108.9380	$1,108.94	$1,108.95	$1,108.90