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	$19.98	12.664%	$22.5103	$22.51	$22.50	$22.50
Purchase #2	$73.67	8.674%	$80.0601	$80.06	$80.05	$80.10
Purchase #3	$231.50	9.174%	$252.7378	$252.74	$252.75	$252.70
Purchase #4	$139.58	3.670%	$144.7026	$144.70	$144.70	$144.70
Purchase #5	$190.53	3.148%	$196.5279	$196.53	$196.55	$196.50
Purchase #6	$102.64	8.675%	$111.544	$111.54	$111.55	$111.50
Purchase #7	$198.94	4.710%	$208.3101	$208.31	$208.30	$208.30
7 purchase totals =	$956.84		$1,016.3928	$1,016.39	$1,016.40	$1,016.30