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	$70.54	11.172%	$78.4207	$78.42	$78.40	$78.40
Purchase #2	$134.71	3.236%	$139.0692	$139.07	$139.05	$139.10
Purchase #3	$148.54	8.118%	$160.5985	$160.60	$160.60	$160.60
Purchase #4	$248.47	8.688%	$270.0571	$270.06	$270.05	$270.10
Purchase #5	$50.85	4.695%	$53.2374	$53.24	$53.25	$53.20
Purchase #6	$147.50	12.220%	$165.5245	$165.52	$165.50	$165.50
Purchase #7	$238.71	9.508%	$261.4065	$261.41	$261.40	$261.40
7 purchase totals =	$1,039.32		$1,128.3139	$1,128.32	$1,128.25	$1,128.30