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	$171.48	4.564%	$179.3063	$179.31	$179.30	$179.30
Purchase #2	$60.43	12.419%	$67.9348	$67.93	$67.95	$67.90
Purchase #3	$98.43	13.297%	$111.5182	$111.52	$111.50	$111.50
Purchase #4	$146.85	12.243%	$164.8288	$164.83	$164.85	$164.80
Purchase #5	$133.51	3.814%	$138.6021	$138.60	$138.60	$138.60
Purchase #6	$224.53	6.438%	$238.9852	$238.99	$239.00	$239.00
Purchase #7	$210.35	4.417%	$219.6412	$219.64	$219.65	$219.60
7 purchase totals =	$1,045.58		$1,120.8166	$1,120.82	$1,120.85	$1,120.70