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	$249.68	7.614%	$268.6906	$268.69	$268.70	$268.70
Purchase #2	$85.39	8.307%	$92.4833	$92.48	$92.50	$92.50
Purchase #3	$41.89	3.432%	$43.3277	$43.33	$43.35	$43.30
Purchase #4	$104.81	6.447%	$111.5671	$111.57	$111.55	$111.60
Purchase #5	$29.90	5.618%	$31.5798	$31.58	$31.60	$31.60
Purchase #6	$163.46	4.494%	$170.8059	$170.81	$170.80	$170.80
Purchase #7	$86.68	10.172%	$95.4971	$95.50	$95.50	$95.50
7 purchase totals =	$761.81		$813.9515	$813.96	$814.00	$814.00