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	$34.98	8.728%	$38.0331	$38.03	$38.05	$38.00
Purchase #2	$78.35	5.536%	$82.6875	$82.69	$82.70	$82.70
Purchase #3	$137.70	5.763%	$145.6357	$145.64	$145.65	$145.60
Purchase #4	$109.78	9.281%	$119.9687	$119.97	$119.95	$120.00
Purchase #5	$146.71	12.470%	$165.0047	$165.00	$165.00	$165.00
Purchase #6	$56.69	9.549%	$62.1033	$62.10	$62.10	$62.10
Purchase #7	$30.69	13.639%	$34.8758	$34.88	$34.90	$34.90
7 purchase totals =	$594.90		$648.3088	$648.31	$648.35	$648.30