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	$78.67	5.320%	$82.8552	$82.86	$82.85	$82.90
Purchase #2	$190.56	11.550%	$212.5697	$212.57	$212.55	$212.60
Purchase #3	$219.57	6.808%	$234.5183	$234.52	$234.50	$234.50
Purchase #4	$56.80	12.358%	$63.8193	$63.82	$63.80	$63.80
Purchase #5	$109.83	5.128%	$115.4621	$115.46	$115.45	$115.50
Purchase #6	$132.39	9.585%	$145.0796	$145.08	$145.10	$145.10
Purchase #7	$94.56	9.596%	$103.634	$103.63	$103.65	$103.60
7 purchase totals =	$882.38		$957.9382	$957.94	$957.90	$958.00