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	$165.40	12.110%	$185.4299	$185.43	$185.45	$185.40
Purchase #2	$81.72	5.285%	$86.0389	$86.04	$86.05	$86.00
Purchase #3	$149.46	11.471%	$166.6046	$166.60	$166.60	$166.60
Purchase #4	$18.65	13.388%	$21.1469	$21.15	$21.15	$21.10
Purchase #5	$73.42	11.108%	$81.5755	$81.58	$81.60	$81.60
Purchase #6	$91.53	11.856%	$102.3818	$102.38	$102.40	$102.40
Purchase #7	$118.84	5.542%	$125.4261	$125.43	$125.45	$125.40
7 purchase totals =	$699.02		$768.6037	$768.61	$768.70	$768.50