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	$168.69	7.696%	$181.6724	$181.67	$181.65	$181.70
Purchase #2	$40.25	5.745%	$42.5624	$42.56	$42.55	$42.60
Purchase #3	$119.39	13.602%	$135.6294	$135.63	$135.65	$135.60
Purchase #4	$65.98	6.171%	$70.0516	$70.05	$70.05	$70.10
Purchase #5	$173.43	3.480%	$179.4654	$179.47	$179.45	$179.50
Purchase #6	$127.56	13.327%	$144.5599	$144.56	$144.55	$144.60
Purchase #7	$156.55	6.177%	$166.2201	$166.22	$166.20	$166.20
7 purchase totals =	$851.85		$920.1612	$920.16	$920.10	$920.30