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	$227.67	12.795%	$256.8004	$256.80	$256.80	$256.80
Purchase #2	$153.36	10.498%	$169.4597	$169.46	$169.45	$169.50
Purchase #3	$18.36	9.766%	$20.153	$20.15	$20.15	$20.20
Purchase #4	$228.95	7.173%	$245.3726	$245.37	$245.35	$245.40
Purchase #5	$122.44	13.549%	$139.0294	$139.03	$139.05	$139.00
Purchase #6	$128.69	10.748%	$142.5216	$142.52	$142.50	$142.50
Purchase #7	$157.83	12.418%	$177.4293	$177.43	$177.45	$177.40
7 purchase totals =	$1,037.30		$1,150.7660	$1,150.76	$1,150.75	$1,150.80