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	$238.77	12.538%	$268.707	$268.71	$268.70	$268.70
Purchase #2	$203.56	6.469%	$216.7283	$216.73	$216.75	$216.70
Purchase #3	$142.53	8.861%	$155.1596	$155.16	$155.15	$155.20
Purchase #4	$60.51	11.139%	$67.2502	$67.25	$67.25	$67.30
Purchase #5	$140.93	12.561%	$158.6322	$158.63	$158.65	$158.60
Purchase #6	$138.61	3.263%	$143.1328	$143.13	$143.15	$143.10
Purchase #7	$82.26	10.587%	$90.9689	$90.97	$90.95	$91.00
7 purchase totals =	$1,007.17		$1,100.5790	$1,100.58	$1,100.60	$1,100.60