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	$185.78	12.233%	$208.5065	$208.51	$208.50	$208.50
Purchase #2	$151.49	12.566%	$170.5262	$170.53	$170.55	$170.50
Purchase #3	$123.31	6.571%	$131.4127	$131.41	$131.40	$131.40
Purchase #4	$144.42	13.857%	$164.4323	$164.43	$164.45	$164.40
Purchase #5	$83.54	5.546%	$88.1731	$88.17	$88.15	$88.20
Purchase #6	$165.51	5.596%	$174.7719	$174.77	$174.75	$174.80
Purchase #7	$181.98	11.750%	$203.3627	$203.36	$203.35	$203.40
7 purchase totals =	$1,036.03		$1,141.1854	$1,141.18	$1,141.15	$1,141.20