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	$159.76	3.130%	$164.7605	$164.76	$164.75	$164.80
Purchase #2	$118.84	8.735%	$129.2207	$129.22	$129.20	$129.20
Purchase #3	$177.37	9.289%	$193.8459	$193.85	$193.85	$193.80
Purchase #4	$145.86	12.847%	$164.5986	$164.60	$164.60	$164.60
Purchase #5	$88.34	13.479%	$100.2473	$100.25	$100.25	$100.20
Purchase #6	$202.94	6.130%	$215.3802	$215.38	$215.40	$215.40
Purchase #7	$107.43	9.353%	$117.4779	$117.48	$117.50	$117.50
7 purchase totals =	$1,000.54		$1,085.5311	$1,085.54	$1,085.55	$1,085.50