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	$225.40	11.605%	$251.5577	$251.56	$251.55	$251.60
Purchase #2	$17.73	4.463%	$18.5213	$18.52	$18.50	$18.50
Purchase #3	$176.32	5.216%	$185.5169	$185.52	$185.50	$185.50
Purchase #4	$132.62	3.577%	$137.3638	$137.36	$137.35	$137.40
Purchase #5	$32.31	4.490%	$33.7607	$33.76	$33.75	$33.80
Purchase #6	$200.40	4.170%	$208.7567	$208.76	$208.75	$208.80
Purchase #7	$78.76	5.378%	$82.9957	$83.00	$83.00	$83.00
7 purchase totals =	$863.54		$918.4728	$918.48	$918.40	$918.60