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	$198.72	13.400%	$225.3485	$225.35	$225.35	$225.30
Purchase #2	$40.73	4.398%	$42.5213	$42.52	$42.50	$42.50
Purchase #3	$176.83	5.496%	$186.5486	$186.55	$186.55	$186.50
Purchase #4	$115.55	10.615%	$127.8156	$127.82	$127.80	$127.80
Purchase #5	$93.52	3.319%	$96.6239	$96.62	$96.60	$96.60
Purchase #6	$163.81	5.368%	$172.6033	$172.60	$172.60	$172.60
Purchase #7	$36.50	7.471%	$39.2269	$39.23	$39.25	$39.20
7 purchase totals =	$825.66		$890.6881	$890.69	$890.65	$890.50