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	$69.27	13.579%	$78.6762	$78.68	$78.70	$78.70
Purchase #2	$108.56	9.170%	$118.515	$118.52	$118.50	$118.50
Purchase #3	$8.27	6.533%	$8.8103	$8.81	$8.80	$8.80
Purchase #4	$118.37	11.405%	$131.8701	$131.87	$131.85	$131.90
Purchase #5	$190.33	11.232%	$211.7079	$211.71	$211.70	$211.70
Purchase #6	$162.29	10.866%	$179.9244	$179.92	$179.90	$179.90
Purchase #7	$230.62	8.178%	$249.4801	$249.48	$249.50	$249.50
7 purchase totals =	$887.71		$978.9840	$978.99	$978.95	$979.00