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	$79.93	5.435%	$84.2742	$84.27	$84.25	$84.30
Purchase #2	$132.56	12.136%	$148.6475	$148.65	$148.65	$148.60
Purchase #3	$235.54	6.396%	$250.6051	$250.61	$250.60	$250.60
Purchase #4	$150.59	3.213%	$155.4285	$155.43	$155.45	$155.40
Purchase #5	$167.67	5.510%	$176.9086	$176.91	$176.90	$176.90
Purchase #6	$84.60	4.196%	$88.1498	$88.15	$88.15	$88.10
Purchase #7	$75.42	13.503%	$85.604	$85.60	$85.60	$85.60
7 purchase totals =	$926.31		$989.6177	$989.62	$989.60	$989.50