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	$179.72	4.326%	$187.4947	$187.49	$187.50	$187.50
Purchase #2	$84.60	9.288%	$92.4576	$92.46	$92.45	$92.50
Purchase #3	$36.48	10.812%	$40.4242	$40.42	$40.40	$40.40
Purchase #4	$74.53	10.167%	$82.1075	$82.11	$82.10	$82.10
Purchase #5	$185.52	3.676%	$192.3397	$192.34	$192.35	$192.30
Purchase #6	$37.85	13.462%	$42.9454	$42.95	$42.95	$42.90
Purchase #7	$39.69	9.470%	$43.4486	$43.45	$43.45	$43.40
7 purchase totals =	$638.39		$681.2177	$681.22	$681.20	$681.10