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	$90.86	10.686%	$100.5693	$100.57	$100.55	$100.60
Purchase #2	$170.97	7.195%	$183.2713	$183.27	$183.25	$183.30
Purchase #3	$156.73	4.316%	$163.4945	$163.49	$163.50	$163.50
Purchase #4	$231.32	11.322%	$257.5101	$257.51	$257.50	$257.50
Purchase #5	$83.99	6.601%	$89.5342	$89.53	$89.55	$89.50
Purchase #6	$12.52	10.846%	$13.8779	$13.88	$13.90	$13.90
Purchase #7	$48.31	10.234%	$53.254	$53.25	$53.25	$53.30
7 purchase totals =	$794.70		$861.5113	$861.50	$861.50	$861.60