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	$133.93	10.649%	$148.1922	$148.19	$148.20	$148.20
Purchase #2	$244.44	5.747%	$258.488	$258.49	$258.50	$258.50
Purchase #3	$171.60	11.166%	$190.7609	$190.76	$190.75	$190.80
Purchase #4	$98.36	6.210%	$104.4682	$104.47	$104.45	$104.50
Purchase #5	$38.86	11.506%	$43.3312	$43.33	$43.35	$43.30
Purchase #6	$71.93	9.367%	$78.6677	$78.67	$78.65	$78.70
Purchase #7	$51.80	5.764%	$54.7858	$54.79	$54.80	$54.80
7 purchase totals =	$810.92		$878.6940	$878.70	$878.70	$878.80