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	$45.86	12.541%	$51.6113	$51.61	$51.60	$51.60
Purchase #2	$118.77	13.405%	$134.6911	$134.69	$134.70	$134.70
Purchase #3	$137.55	9.843%	$151.089	$151.09	$151.10	$151.10
Purchase #4	$97.64	3.607%	$101.1619	$101.16	$101.15	$101.20
Purchase #5	$161.85	6.114%	$171.7455	$171.75	$171.75	$171.70
Purchase #6	$176.48	11.352%	$196.514	$196.51	$196.50	$196.50
Purchase #7	$126.48	7.538%	$136.0141	$136.01	$136.00	$136.00
7 purchase totals =	$864.63		$942.8269	$942.82	$942.80	$942.80