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	$110.41	9.203%	$120.571	$120.57	$120.55	$120.60
Purchase #2	$118.71	7.434%	$127.5349	$127.53	$127.55	$127.50
Purchase #3	$222.61	7.246%	$238.7403	$238.74	$238.75	$238.70
Purchase #4	$165.26	6.708%	$176.3456	$176.35	$176.35	$176.30
Purchase #5	$38.68	5.763%	$40.9091	$40.91	$40.90	$40.90
Purchase #6	$97.56	5.470%	$102.8965	$102.90	$102.90	$102.90
Purchase #7	$82.88	9.493%	$90.7478	$90.75	$90.75	$90.70
7 purchase totals =	$836.11		$897.7452	$897.75	$897.75	$897.60