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	$52.42	6.813%	$55.9914	$55.99	$56.00	$56.00
Purchase #2	$36.30	12.120%	$40.6996	$40.70	$40.70	$40.70
Purchase #3	$65.88	9.299%	$72.0062	$72.01	$72.00	$72.00
Purchase #4	$137.89	10.533%	$152.414	$152.41	$152.40	$152.40
Purchase #5	$44.77	4.401%	$46.7403	$46.74	$46.75	$46.70
Purchase #6	$105.69	9.217%	$115.4314	$115.43	$115.45	$115.40
Purchase #7	$152.94	12.191%	$171.5849	$171.58	$171.60	$171.60
7 purchase totals =	$595.89		$654.8678	$654.86	$654.90	$654.80