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	$67.38	5.834%	$71.3109	$71.31	$71.30	$71.30
Purchase #2	$186.39	5.203%	$196.0879	$196.09	$196.10	$196.10
Purchase #3	$127.53	9.541%	$139.6976	$139.70	$139.70	$139.70
Purchase #4	$201.52	13.359%	$228.4411	$228.44	$228.45	$228.40
Purchase #5	$198.34	12.120%	$222.3788	$222.38	$222.40	$222.40
Purchase #6	$247.42	10.860%	$274.2898	$274.29	$274.30	$274.30
Purchase #7	$159.32	3.252%	$164.5011	$164.50	$164.50	$164.50
7 purchase totals =	$1,187.90		$1,296.7072	$1,296.71	$1,296.75	$1,296.70