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	$248.71	5.150%	$261.5186	$261.52	$261.50	$261.50
Purchase #2	$64.72	9.874%	$71.1105	$71.11	$71.10	$71.10
Purchase #3	$248.49	5.128%	$261.2326	$261.23	$261.25	$261.20
Purchase #4	$179.90	4.522%	$188.0351	$188.04	$188.05	$188.00
Purchase #5	$166.60	4.184%	$173.5705	$173.57	$173.55	$173.60
Purchase #6	$62.56	4.580%	$65.4252	$65.43	$65.45	$65.40
Purchase #7	$132.34	6.480%	$140.9156	$140.92	$140.90	$140.90
7 purchase totals =	$1,103.32		$1,161.8081	$1,161.82	$1,161.80	$1,161.70