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	$168.44	9.708%	$184.7922	$184.79	$184.80	$184.80
Purchase #2	$142.67	10.524%	$157.6846	$157.68	$157.70	$157.70
Purchase #3	$93.91	10.544%	$103.8119	$103.81	$103.80	$103.80
Purchase #4	$166.44	10.259%	$183.5151	$183.52	$183.50	$183.50
Purchase #5	$42.72	3.123%	$44.0541	$44.05	$44.05	$44.10
Purchase #6	$180.44	8.706%	$196.1491	$196.15	$196.15	$196.10
Purchase #7	$141.69	7.123%	$151.7826	$151.78	$151.80	$151.80
7 purchase totals =	$936.31		$1,021.7896	$1,021.78	$1,021.80	$1,021.80