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	$240.79	9.831%	$264.4621	$264.46	$264.45	$264.50
Purchase #2	$117.86	5.119%	$123.8933	$123.89	$123.90	$123.90
Purchase #3	$240.64	12.532%	$270.797	$270.80	$270.80	$270.80
Purchase #4	$136.90	5.346%	$144.2187	$144.22	$144.20	$144.20
Purchase #5	$92.83	8.252%	$100.4903	$100.49	$100.50	$100.50
Purchase #6	$140.94	9.396%	$154.1827	$154.18	$154.20	$154.20
Purchase #7	$77.97	9.821%	$85.6274	$85.63	$85.65	$85.60
7 purchase totals =	$1,047.93		$1,143.6715	$1,143.67	$1,143.70	$1,143.70