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	$246.82	7.529%	$265.4031	$265.40	$265.40	$265.40
Purchase #2	$131.35	9.470%	$143.7888	$143.79	$143.80	$143.80
Purchase #3	$27.52	3.492%	$28.481	$28.48	$28.50	$28.50
Purchase #4	$224.36	3.472%	$232.1498	$232.15	$232.15	$232.10
Purchase #5	$17.72	4.531%	$18.5229	$18.52	$18.50	$18.50
Purchase #6	$103.77	7.108%	$111.146	$111.15	$111.15	$111.10
Purchase #7	$194.68	13.753%	$221.4543	$221.45	$221.45	$221.50
7 purchase totals =	$946.22		$1,020.9459	$1,020.94	$1,020.95	$1,020.90