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	$134.45	3.295%	$138.8801	$138.88	$138.90	$138.90
Purchase #2	$107.66	3.484%	$111.4109	$111.41	$111.40	$111.40
Purchase #3	$103.39	7.321%	$110.9592	$110.96	$110.95	$111.00
Purchase #4	$182.68	4.640%	$191.1564	$191.16	$191.15	$191.20
Purchase #5	$184.56	11.505%	$205.7936	$205.79	$205.80	$205.80
Purchase #6	$64.91	4.315%	$67.7109	$67.71	$67.70	$67.70
Purchase #7	$153.76	12.620%	$173.1645	$173.16	$173.15	$173.20
7 purchase totals =	$931.41		$999.0756	$999.07	$999.05	$999.20