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	$156.41	3.708%	$162.2097	$162.21	$162.20	$162.20
Purchase #2	$210.25	12.228%	$235.9594	$235.96	$235.95	$236.00
Purchase #3	$104.87	9.551%	$114.8861	$114.89	$114.90	$114.90
Purchase #4	$111.60	4.167%	$116.2504	$116.25	$116.25	$116.30
Purchase #5	$67.87	5.298%	$71.4658	$71.47	$71.45	$71.50
Purchase #6	$71.76	9.532%	$78.6002	$78.60	$78.60	$78.60
Purchase #7	$65.43	9.236%	$71.4731	$71.47	$71.45	$71.50
7 purchase totals =	$788.19		$850.8447	$850.85	$850.80	$851.00