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	$140.71	3.318%	$145.3788	$145.38	$145.40	$145.40
Purchase #2	$90.52	11.509%	$100.9379	$100.94	$100.95	$100.90
Purchase #3	$65.58	8.661%	$71.2599	$71.26	$71.25	$71.30
Purchase #4	$90.62	5.789%	$95.866	$95.87	$95.85	$95.90
Purchase #5	$134.76	11.522%	$150.287	$150.29	$150.30	$150.30
Purchase #6	$73.71	4.341%	$76.9098	$76.91	$76.90	$76.90
Purchase #7	$150.58	11.613%	$168.0669	$168.07	$168.05	$168.10
7 purchase totals =	$746.48		$808.7063	$808.72	$808.70	$808.80