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	$45.68	12.215%	$51.2598	$51.26	$51.25	$51.30
Purchase #2	$111.31	4.438%	$116.2499	$116.25	$116.25	$116.20
Purchase #3	$104.54	5.137%	$109.9102	$109.91	$109.90	$109.90
Purchase #4	$76.46	13.241%	$86.5841	$86.58	$86.60	$86.60
Purchase #5	$24.25	4.449%	$25.3289	$25.33	$25.35	$25.30
Purchase #6	$127.39	7.264%	$136.6436	$136.64	$136.65	$136.60
Purchase #7	$124.35	3.695%	$128.9447	$128.94	$128.95	$128.90
7 purchase totals =	$613.98		$654.9212	$654.91	$654.95	$654.80