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	$229.51	6.576%	$244.6026	$244.60	$244.60	$244.60
Purchase #2	$19.43	4.182%	$20.2426	$20.24	$20.25	$20.20
Purchase #3	$165.66	13.158%	$187.4575	$187.46	$187.45	$187.50
Purchase #4	$72.31	12.703%	$81.4955	$81.50	$81.50	$81.50
Purchase #5	$162.60	12.506%	$182.9348	$182.93	$182.95	$182.90
Purchase #6	$233.58	5.522%	$246.4783	$246.48	$246.50	$246.50
Purchase #7	$129.84	5.304%	$136.7267	$136.73	$136.75	$136.70
7 purchase totals =	$1,012.93		$1,099.9380	$1,099.94	$1,100.00	$1,099.90