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	$106.97	12.375%	$120.2075	$120.21	$120.20	$120.20
Purchase #2	$179.80	11.138%	$199.8261	$199.83	$199.85	$199.80
Purchase #3	$236.37	13.480%	$268.2327	$268.23	$268.25	$268.20
Purchase #4	$125.59	13.543%	$142.5987	$142.60	$142.60	$142.60
Purchase #5	$54.83	13.291%	$62.1175	$62.12	$62.10	$62.10
Purchase #6	$89.58	12.388%	$100.6772	$100.68	$100.70	$100.70
Purchase #7	$196.77	4.822%	$206.2582	$206.26	$206.25	$206.30
7 purchase totals =	$989.91		$1,099.9179	$1,099.93	$1,099.95	$1,099.90