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	$78.71	5.180%	$82.7872	$82.79	$82.80	$82.80
Purchase #2	$157.96	4.178%	$164.5596	$164.56	$164.55	$164.60
Purchase #3	$55.29	10.824%	$61.2746	$61.27	$61.25	$61.30
Purchase #4	$46.85	11.553%	$52.2626	$52.26	$52.25	$52.30
Purchase #5	$105.50	6.834%	$112.7099	$112.71	$112.70	$112.70
Purchase #6	$8.25	11.242%	$9.1775	$9.18	$9.20	$9.20
Purchase #7	$179.46	6.265%	$190.7032	$190.70	$190.70	$190.70
7 purchase totals =	$632.02		$673.4746	$673.47	$673.45	$673.60