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	$165.45	13.677%	$188.0786	$188.08	$188.10	$188.10
Purchase #2	$201.52	6.119%	$213.851	$213.85	$213.85	$213.90
Purchase #3	$51.49	11.206%	$57.26	$57.26	$57.25	$57.30
Purchase #4	$36.64	6.716%	$39.1007	$39.10	$39.10	$39.10
Purchase #5	$194.32	5.799%	$205.5886	$205.59	$205.60	$205.60
Purchase #6	$38.72	11.608%	$43.2146	$43.21	$43.20	$43.20
Purchase #7	$98.54	13.440%	$111.7838	$111.78	$111.80	$111.80
7 purchase totals =	$786.68		$858.8773	$858.87	$858.90	$859.00