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	$157.89	13.207%	$178.7425	$178.74	$178.75	$178.70
Purchase #2	$54.65	12.180%	$61.3064	$61.31	$61.30	$61.30
Purchase #3	$136.86	10.506%	$151.2385	$151.24	$151.25	$151.20
Purchase #4	$103.83	9.661%	$113.861	$113.86	$113.85	$113.90
Purchase #5	$97.97	7.259%	$105.0816	$105.08	$105.10	$105.10
Purchase #6	$159.36	12.641%	$179.5047	$179.50	$179.50	$179.50
Purchase #7	$7.59	11.357%	$8.452	$8.45	$8.45	$8.50
7 purchase totals =	$718.15		$798.1867	$798.18	$798.20	$798.20