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	$200.66	5.660%	$212.0174	$212.02	$212.00	$212.00
Purchase #2	$73.95	11.256%	$82.2738	$82.27	$82.25	$82.30
Purchase #3	$74.93	7.411%	$80.4831	$80.48	$80.50	$80.50
Purchase #4	$38.98	3.114%	$40.1938	$40.19	$40.20	$40.20
Purchase #5	$141.33	11.808%	$158.0182	$158.02	$158.00	$158.00
Purchase #6	$66.88	10.852%	$74.1378	$74.14	$74.15	$74.10
Purchase #7	$202.25	10.164%	$222.8067	$222.81	$222.80	$222.80
7 purchase totals =	$798.98		$869.9308	$869.93	$869.90	$869.90