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	$158.32	13.410%	$179.5507	$179.55	$179.55	$179.60
Purchase #2	$76.46	7.155%	$81.9307	$81.93	$81.95	$81.90
Purchase #3	$20.54	6.379%	$21.8502	$21.85	$21.85	$21.90
Purchase #4	$17.50	5.547%	$18.4707	$18.47	$18.45	$18.50
Purchase #5	$99.58	12.614%	$112.141	$112.14	$112.15	$112.10
Purchase #6	$113.30	3.200%	$116.9256	$116.93	$116.95	$116.90
Purchase #7	$135.86	4.818%	$142.4057	$142.41	$142.40	$142.40
7 purchase totals =	$621.56		$673.2746	$673.28	$673.30	$673.30