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	$139.45	6.472%	$148.4752	$148.48	$148.50	$148.50
Purchase #2	$69.80	12.477%	$78.5089	$78.51	$78.50	$78.50
Purchase #3	$131.60	9.480%	$144.0757	$144.08	$144.10	$144.10
Purchase #4	$192.82	8.298%	$208.8202	$208.82	$208.80	$208.80
Purchase #5	$202.61	7.233%	$217.2648	$217.26	$217.25	$217.30
Purchase #6	$130.69	10.577%	$144.5131	$144.51	$144.50	$144.50
Purchase #7	$191.58	9.258%	$209.3165	$209.32	$209.30	$209.30
7 purchase totals =	$1,058.55		$1,150.9744	$1,150.98	$1,150.95	$1,151.00