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	$145.52	13.176%	$164.6937	$164.69	$164.70	$164.70
Purchase #2	$173.63	13.356%	$196.82	$196.82	$196.80	$196.80
Purchase #3	$127.98	11.102%	$142.1883	$142.19	$142.20	$142.20
Purchase #4	$30.57	4.703%	$32.0077	$32.01	$32.00	$32.00
Purchase #5	$226.70	11.729%	$253.2896	$253.29	$253.30	$253.30
Purchase #6	$153.30	11.689%	$171.2192	$171.22	$171.20	$171.20
Purchase #7	$19.58	13.360%	$22.1959	$22.20	$22.20	$22.20
7 purchase totals =	$877.28		$982.4144	$982.42	$982.40	$982.40