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	$71.49	9.642%	$78.3831	$78.38	$78.40	$78.40
Purchase #2	$51.71	8.348%	$56.0268	$56.03	$56.05	$56.00
Purchase #3	$133.84	13.710%	$152.1895	$152.19	$152.20	$152.20
Purchase #4	$182.94	4.474%	$191.1247	$191.12	$191.10	$191.10
Purchase #5	$86.82	13.822%	$98.8203	$98.82	$98.80	$98.80
Purchase #6	$51.32	4.443%	$53.6001	$53.60	$53.60	$53.60
Purchase #7	$116.32	12.669%	$131.0566	$131.06	$131.05	$131.10
7 purchase totals =	$694.44		$761.2011	$761.20	$761.20	$761.20