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	$99.61	12.270%	$111.8321	$111.83	$111.85	$111.80
Purchase #2	$85.47	9.682%	$93.7452	$93.75	$93.75	$93.70
Purchase #3	$44.77	4.238%	$46.6674	$46.67	$46.65	$46.70
Purchase #4	$146.75	5.420%	$154.7039	$154.70	$154.70	$154.70
Purchase #5	$123.87	12.119%	$138.8818	$138.88	$138.90	$138.90
Purchase #6	$69.35	4.237%	$72.2884	$72.29	$72.30	$72.30
Purchase #7	$67.54	7.655%	$72.7102	$72.71	$72.70	$72.70
7 purchase totals =	$637.36		$690.8290	$690.83	$690.85	$690.80