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	$147.60	11.211%	$164.1474	$164.15	$164.15	$164.10
Purchase #2	$110.25	6.401%	$117.3071	$117.31	$117.30	$117.30
Purchase #3	$173.79	9.247%	$189.8604	$189.86	$189.85	$189.90
Purchase #4	$229.58	13.796%	$261.2529	$261.25	$261.25	$261.30
Purchase #5	$85.52	12.328%	$96.0629	$96.06	$96.05	$96.10
Purchase #6	$127.60	13.214%	$144.4611	$144.46	$144.45	$144.50
Purchase #7	$60.56	9.561%	$66.3501	$66.35	$66.35	$66.40
7 purchase totals =	$934.90		$1,039.4419	$1,039.44	$1,039.40	$1,039.60