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	$42.41	3.857%	$44.0458	$44.05	$44.05	$44.00
Purchase #2	$131.86	7.315%	$141.5056	$141.51	$141.50	$141.50
Purchase #3	$208.41	8.409%	$225.9352	$225.94	$225.95	$225.90
Purchase #4	$120.39	9.491%	$131.8162	$131.82	$131.80	$131.80
Purchase #5	$156.55	9.259%	$171.045	$171.05	$171.05	$171.00
Purchase #6	$230.39	7.773%	$248.2982	$248.30	$248.30	$248.30
Purchase #7	$127.66	8.262%	$138.2073	$138.21	$138.20	$138.20
7 purchase totals =	$1,017.67		$1,100.8533	$1,100.88	$1,100.85	$1,100.70