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	$110.34	12.842%	$124.5099	$124.51	$124.50	$124.50
Purchase #2	$81.62	10.592%	$90.2652	$90.27	$90.25	$90.30
Purchase #3	$19.45	13.496%	$22.075	$22.08	$22.10	$22.10
Purchase #4	$228.32	9.280%	$249.5081	$249.51	$249.50	$249.50
Purchase #5	$110.80	6.786%	$118.3189	$118.32	$118.30	$118.30
Purchase #6	$224.51	3.601%	$232.5946	$232.59	$232.60	$232.60
Purchase #7	$56.93	10.179%	$62.7249	$62.72	$62.70	$62.70
7 purchase totals =	$831.97		$899.9966	$900.00	$899.95	$900.00