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	$94.88	4.571%	$99.217	$99.22	$99.20	$99.20
Purchase #2	$111.62	3.142%	$115.1271	$115.13	$115.15	$115.10
Purchase #3	$177.53	4.720%	$185.9094	$185.91	$185.90	$185.90
Purchase #4	$85.71	4.354%	$89.4418	$89.44	$89.45	$89.40
Purchase #5	$48.57	4.183%	$50.6017	$50.60	$50.60	$50.60
Purchase #6	$216.88	10.149%	$238.8912	$238.89	$238.90	$238.90
Purchase #7	$127.31	4.234%	$132.7003	$132.70	$132.70	$132.70
7 purchase totals =	$862.50		$911.8885	$911.89	$911.90	$911.80