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	$177.58	6.693%	$189.4654	$189.47	$189.45	$189.50
Purchase #2	$209.61	5.320%	$220.7613	$220.76	$220.75	$220.80
Purchase #3	$230.88	4.314%	$240.8402	$240.84	$240.85	$240.80
Purchase #4	$250.85	11.123%	$278.752	$278.75	$278.75	$278.80
Purchase #5	$85.35	5.819%	$90.3165	$90.32	$90.30	$90.30
Purchase #6	$162.79	6.774%	$173.8174	$173.82	$173.80	$173.80
Purchase #7	$69.43	13.437%	$78.7593	$78.76	$78.75	$78.80
7 purchase totals =	$1,186.49		$1,272.7121	$1,272.72	$1,272.65	$1,272.80