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	$137.30	8.194%	$148.5504	$148.55	$148.55	$148.60
Purchase #2	$46.76	10.407%	$51.6263	$51.63	$51.65	$51.60
Purchase #3	$127.73	9.716%	$140.1402	$140.14	$140.15	$140.10
Purchase #4	$180.82	7.436%	$194.2658	$194.27	$194.25	$194.30
Purchase #5	$6.65	10.161%	$7.3257	$7.33	$7.35	$7.30
Purchase #6	$11.43	6.477%	$12.1703	$12.17	$12.15	$12.20
Purchase #7	$109.65	3.138%	$113.0908	$113.09	$113.10	$113.10
7 purchase totals =	$620.34		$667.1695	$667.18	$667.20	$667.20