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	$200.75	10.817%	$222.4651	$222.47	$222.45	$222.50
Purchase #2	$91.76	12.600%	$103.3218	$103.32	$103.30	$103.30
Purchase #3	$112.48	6.255%	$119.5156	$119.52	$119.50	$119.50
Purchase #4	$124.41	8.210%	$134.6241	$134.62	$134.60	$134.60
Purchase #5	$109.63	6.150%	$116.3722	$116.37	$116.35	$116.40
Purchase #6	$82.40	8.832%	$89.6776	$89.68	$89.70	$89.70
Purchase #7	$171.95	10.303%	$189.666	$189.67	$189.65	$189.70
7 purchase totals =	$893.38		$975.6424	$975.65	$975.55	$975.70