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	$31.65	3.108%	$32.6337	$32.63	$32.65	$32.60
Purchase #2	$217.70	11.126%	$241.9213	$241.92	$241.90	$241.90
Purchase #3	$83.60	6.696%	$89.1979	$89.20	$89.20	$89.20
Purchase #4	$214.86	3.502%	$222.3844	$222.38	$222.40	$222.40
Purchase #5	$157.84	5.458%	$166.4549	$166.45	$166.45	$166.50
Purchase #6	$120.99	8.190%	$130.8991	$130.90	$130.90	$130.90
Purchase #7	$70.81	10.437%	$78.2004	$78.20	$78.20	$78.20
7 purchase totals =	$897.45		$961.6917	$961.68	$961.70	$961.70