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	$51.74	5.673%	$54.6752	$54.68	$54.70	$54.70
Purchase #2	$206.63	4.263%	$215.4386	$215.44	$215.45	$215.40
Purchase #3	$17.25	4.693%	$18.0595	$18.06	$18.05	$18.10
Purchase #4	$31.30	7.440%	$33.6287	$33.63	$33.65	$33.60
Purchase #5	$32.72	10.520%	$36.1621	$36.16	$36.15	$36.20
Purchase #6	$158.70	6.191%	$168.5251	$168.53	$168.55	$168.50
Purchase #7	$241.32	7.743%	$260.0054	$260.01	$260.00	$260.00
7 purchase totals =	$739.66		$786.4946	$786.51	$786.55	$786.50