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	$232.33	3.251%	$239.883	$239.88	$239.90	$239.90
Purchase #2	$58.89	11.593%	$65.7171	$65.72	$65.70	$65.70
Purchase #3	$40.72	4.641%	$42.6098	$42.61	$42.60	$42.60
Purchase #4	$227.42	12.458%	$255.752	$255.75	$255.75	$255.80
Purchase #5	$196.49	5.581%	$207.4561	$207.46	$207.45	$207.50
Purchase #6	$198.62	3.135%	$204.8467	$204.85	$204.85	$204.80
Purchase #7	$75.65	9.331%	$82.7089	$82.71	$82.70	$82.70
7 purchase totals =	$1,030.12		$1,098.9736	$1,098.98	$1,098.95	$1,099.00