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	$102.46	3.178%	$105.7162	$105.72	$105.70	$105.70
Purchase #2	$64.36	8.701%	$69.96	$69.96	$69.95	$70.00
Purchase #3	$40.59	11.643%	$45.3159	$45.32	$45.30	$45.30
Purchase #4	$156.60	3.632%	$162.2877	$162.29	$162.30	$162.30
Purchase #5	$149.62	6.652%	$159.5727	$159.57	$159.55	$159.60
Purchase #6	$227.97	10.175%	$251.1659	$251.17	$251.15	$251.20
Purchase #7	$64.33	12.586%	$72.4266	$72.43	$72.45	$72.40
7 purchase totals =	$805.93		$866.4450	$866.46	$866.40	$866.50