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	$150.70	11.798%	$168.4796	$168.48	$168.50	$168.50
Purchase #2	$5.39	9.162%	$5.8838	$5.88	$5.90	$5.90
Purchase #3	$79.92	13.794%	$90.9442	$90.94	$90.95	$90.90
Purchase #4	$63.69	12.775%	$71.8264	$71.83	$71.85	$71.80
Purchase #5	$166.47	13.571%	$189.0616	$189.06	$189.05	$189.10
Purchase #6	$6.41	10.480%	$7.0818	$7.08	$7.10	$7.10
Purchase #7	$127.58	11.387%	$142.1075	$142.11	$142.10	$142.10
7 purchase totals =	$600.16		$675.3849	$675.38	$675.45	$675.40