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	$80.77	9.256%	$88.2461	$88.25	$88.25	$88.20
Purchase #2	$71.42	4.149%	$74.3832	$74.38	$74.40	$74.40
Purchase #3	$46.40	11.113%	$51.5564	$51.56	$51.55	$51.60
Purchase #4	$244.90	12.493%	$275.4954	$275.50	$275.50	$275.50
Purchase #5	$186.98	6.128%	$198.4381	$198.44	$198.45	$198.40
Purchase #6	$230.42	10.432%	$254.4574	$254.46	$254.45	$254.50
Purchase #7	$162.57	10.112%	$179.0091	$179.01	$179.00	$179.00
7 purchase totals =	$1,023.46		$1,121.5857	$1,121.60	$1,121.60	$1,121.60