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	$35.87	6.695%	$38.2715	$38.27	$38.25	$38.30
Purchase #2	$211.46	3.597%	$219.0662	$219.07	$219.05	$219.10
Purchase #3	$25.26	6.294%	$26.8499	$26.85	$26.85	$26.80
Purchase #4	$111.90	10.466%	$123.6115	$123.61	$123.60	$123.60
Purchase #5	$119.33	3.619%	$123.6486	$123.65	$123.65	$123.60
Purchase #6	$199.52	7.768%	$215.0187	$215.02	$215.00	$215.00
Purchase #7	$24.75	11.328%	$27.5537	$27.55	$27.55	$27.60
7 purchase totals =	$728.09		$774.0201	$774.02	$773.95	$774.00