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	$108.66	7.541%	$116.8541	$116.85	$116.85	$116.90
Purchase #2	$245.90	13.856%	$279.9719	$279.97	$279.95	$280.00
Purchase #3	$59.91	8.541%	$65.0269	$65.03	$65.05	$65.00
Purchase #4	$240.96	3.495%	$249.3816	$249.38	$249.40	$249.40
Purchase #5	$172.89	12.710%	$194.8643	$194.86	$194.85	$194.90
Purchase #6	$46.44	9.111%	$50.6711	$50.67	$50.65	$50.70
Purchase #7	$79.84	3.328%	$82.4971	$82.50	$82.50	$82.50
7 purchase totals =	$954.60		$1,039.2670	$1,039.26	$1,039.25	$1,039.40