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	$110.70	7.407%	$118.8995	$118.90	$118.90	$118.90
Purchase #2	$122.53	3.757%	$127.1335	$127.13	$127.15	$127.10
Purchase #3	$188.59	4.387%	$196.8634	$196.86	$196.85	$196.90
Purchase #4	$48.53	13.394%	$55.0301	$55.03	$55.05	$55.00
Purchase #5	$9.96	11.597%	$11.1151	$11.12	$11.10	$11.10
Purchase #6	$159.97	5.153%	$168.2133	$168.21	$168.20	$168.20
Purchase #7	$247.82	12.617%	$279.0874	$279.09	$279.10	$279.10
7 purchase totals =	$888.10		$956.3423	$956.34	$956.35	$956.30