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	$155.81	6.838%	$166.4643	$166.46	$166.45	$166.50
Purchase #2	$39.66	10.158%	$43.6887	$43.69	$43.70	$43.70
Purchase #3	$107.52	11.567%	$119.9568	$119.96	$119.95	$120.00
Purchase #4	$148.48	13.495%	$168.5174	$168.52	$168.50	$168.50
Purchase #5	$238.62	10.459%	$263.5773	$263.58	$263.60	$263.60
Purchase #6	$180.82	8.581%	$196.3362	$196.34	$196.35	$196.30
Purchase #7	$44.53	8.478%	$48.3053	$48.31	$48.30	$48.30
7 purchase totals =	$915.44		$1,006.8460	$1,006.86	$1,006.85	$1,006.90