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	$19.36	10.826%	$21.4559	$21.46	$21.45	$21.50
Purchase #2	$82.33	12.443%	$92.5743	$92.57	$92.55	$92.60
Purchase #3	$150.83	4.355%	$157.3986	$157.40	$157.40	$157.40
Purchase #4	$67.94	8.786%	$73.9092	$73.91	$73.90	$73.90
Purchase #5	$199.60	10.188%	$219.9352	$219.94	$219.95	$219.90
Purchase #6	$40.89	13.811%	$46.5373	$46.54	$46.55	$46.50
Purchase #7	$177.31	11.855%	$198.3301	$198.33	$198.35	$198.30
7 purchase totals =	$738.26		$810.1406	$810.15	$810.15	$810.10