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	$79.77	3.764%	$82.7725	$82.77	$82.75	$82.80
Purchase #2	$176.32	13.212%	$199.6154	$199.62	$199.60	$199.60
Purchase #3	$226.51	4.627%	$236.9906	$236.99	$237.00	$237.00
Purchase #4	$247.59	5.142%	$260.3211	$260.32	$260.30	$260.30
Purchase #5	$225.37	7.135%	$241.4501	$241.45	$241.45	$241.50
Purchase #6	$28.78	10.385%	$31.7688	$31.77	$31.75	$31.80
Purchase #7	$197.61	12.610%	$222.5286	$222.53	$222.55	$222.50
7 purchase totals =	$1,181.95		$1,275.4471	$1,275.45	$1,275.40	$1,275.50