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	$239.53	12.279%	$268.9419	$268.94	$268.95	$268.90
Purchase #2	$228.43	12.677%	$257.3881	$257.39	$257.40	$257.40
Purchase #3	$207.44	9.688%	$227.5368	$227.54	$227.55	$227.50
Purchase #4	$37.41	9.856%	$41.0971	$41.10	$41.10	$41.10
Purchase #5	$99.25	12.578%	$111.7337	$111.73	$111.75	$111.70
Purchase #6	$96.28	4.432%	$100.5471	$100.55	$100.55	$100.50
Purchase #7	$215.42	8.554%	$233.847	$233.85	$233.85	$233.80
7 purchase totals =	$1,123.76		$1,241.0917	$1,241.10	$1,241.15	$1,240.90