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	$101.95	7.292%	$109.3842	$109.38	$109.40	$109.40
Purchase #2	$225.42	5.845%	$238.5958	$238.60	$238.60	$238.60
Purchase #3	$232.44	7.793%	$250.554	$250.55	$250.55	$250.60
Purchase #4	$60.71	12.723%	$68.4341	$68.43	$68.45	$68.40
Purchase #5	$123.51	11.309%	$137.4777	$137.48	$137.50	$137.50
Purchase #6	$219.93	11.470%	$245.156	$245.16	$245.15	$245.20
Purchase #7	$214.31	5.382%	$225.8442	$225.84	$225.85	$225.80
7 purchase totals =	$1,178.27		$1,275.4460	$1,275.44	$1,275.50	$1,275.50