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	$114.68	4.874%	$120.2695	$120.27	$120.25	$120.30
Purchase #2	$194.71	5.311%	$205.051	$205.05	$205.05	$205.10
Purchase #3	$224.83	5.741%	$237.7375	$237.74	$237.75	$237.70
Purchase #4	$63.97	13.402%	$72.5433	$72.54	$72.55	$72.50
Purchase #5	$36.30	12.789%	$40.9424	$40.94	$40.95	$40.90
Purchase #6	$218.93	9.639%	$240.0327	$240.03	$240.05	$240.00
Purchase #7	$56.41	9.242%	$61.6234	$61.62	$61.60	$61.60
7 purchase totals =	$909.83		$978.1998	$978.19	$978.20	$978.10