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	$59.54	6.645%	$63.4964	$63.50	$63.50	$63.50
Purchase #2	$153.69	9.371%	$168.0923	$168.09	$168.10	$168.10
Purchase #3	$174.98	12.462%	$196.786	$196.79	$196.80	$196.80
Purchase #4	$124.95	8.452%	$135.5108	$135.51	$135.50	$135.50
Purchase #5	$162.64	9.563%	$178.1933	$178.19	$178.20	$178.20
Purchase #6	$30.25	13.794%	$34.4227	$34.42	$34.40	$34.40
Purchase #7	$99.69	11.669%	$111.3228	$111.32	$111.30	$111.30
7 purchase totals =	$805.74		$887.8243	$887.82	$887.80	$887.80