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	$139.97	11.854%	$156.562	$156.56	$156.55	$156.60
Purchase #2	$116.40	3.617%	$120.6102	$120.61	$120.60	$120.60
Purchase #3	$122.29	5.270%	$128.7347	$128.73	$128.75	$128.70
Purchase #4	$242.99	5.153%	$255.5113	$255.51	$255.50	$255.50
Purchase #5	$129.46	8.716%	$140.7437	$140.74	$140.75	$140.70
Purchase #6	$152.93	10.681%	$169.2645	$169.26	$169.25	$169.30
Purchase #7	$184.49	6.568%	$196.6073	$196.61	$196.60	$196.60
7 purchase totals =	$1,088.53		$1,168.0337	$1,168.02	$1,168.00	$1,168.00