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	$197.87	9.358%	$216.3867	$216.39	$216.40	$216.40
Purchase #2	$54.60	5.304%	$57.496	$57.50	$57.50	$57.50
Purchase #3	$88.91	6.303%	$94.514	$94.51	$94.50	$94.50
Purchase #4	$69.70	4.345%	$72.7285	$72.73	$72.75	$72.70
Purchase #5	$32.46	6.396%	$34.5361	$34.54	$34.55	$34.50
Purchase #6	$226.39	10.753%	$250.7337	$250.73	$250.75	$250.70
Purchase #7	$102.54	11.306%	$114.1332	$114.13	$114.15	$114.10
7 purchase totals =	$772.47		$840.5282	$840.53	$840.60	$840.40